diff --git a/src/org/labkey/targetedms/view/instrumentCalendar.jsp b/src/org/labkey/targetedms/view/instrumentCalendar.jsp
index 2e6c35d1a..6fe5b5e73 100644
--- a/src/org/labkey/targetedms/view/instrumentCalendar.jsp
+++ b/src/org/labkey/targetedms/view/instrumentCalendar.jsp
@@ -23,6 +23,7 @@
     {
         dependencies.add("internal/jQuery");
         dependencies.add("targetedms/yearCalendar");
+        dependencies.add("TargetedMS/js/scheduleUtils.js");
     }
 %>
 
@@ -51,8 +52,8 @@
         $('#delete-event').css('display', event.annotation ? '' : 'none');
 
         $('#event-modal input[name="event-description"]').val(event.annotation ? event.annotation.description : '');
-        $('#event-modal input[name="event-start-date"]').val(startDate.getFullYear() + '-' + (startDate.getMonth() + 1 < 10 ? '0' : '') + (startDate.getMonth() + 1) + '-' + (startDate.getDate() < 10 ? '0' : '') + startDate.getDate());
-        $('#event-modal input[name="event-end-date"]').val(endDate.getFullYear() + '-' + (endDate.getMonth() + 1 < 10 ? '0' : '') + (endDate.getMonth() + 1) + '-' + (endDate.getDate() < 10 ? '0' : '') + endDate.getDate());
+        $('#event-modal input[name="event-start-date"]').val(ScheduleUtils.toDateValue(startDate));
+        $('#event-modal input[name="event-end-date"]').val(ScheduleUtils.toDateValue(endDate));
         $('#annotation-save-error').text('');
         $('#event-modal').modal();
     }
diff --git a/test/src/org/labkey/test/tests/targetedms/InstrumentSchedulingTest.java b/test/src/org/labkey/test/tests/targetedms/InstrumentSchedulingTest.java
index 1ce61bf63..ea9905ba9 100644
--- a/test/src/org/labkey/test/tests/targetedms/InstrumentSchedulingTest.java
+++ b/test/src/org/labkey/test/tests/targetedms/InstrumentSchedulingTest.java
@@ -183,6 +183,9 @@ public void testSchedule() throws IOException, CommandException
         {
             String originalStart = getFormElement(START_DATE_TIME_FIELD.findElement(getDriver()));
             String originalEnd = getFormElement(END_DATE_TIME_FIELD.findElement(getDriver()));
+            // Pin the 8AM/5PM defaults so a regression that zeroes or shifts the time is caught even on agents whose timezone would otherwise hide it.
+            assertTrue("Start field should default to 8AM, was: " + originalStart, originalStart.endsWith("T08:00"));
+            assertTrue("End field should default to 5PM, was: " + originalEnd, originalEnd.endsWith("T17:00"));
             // Try scheduling over the first reservation and verify it is blocked
             setFormElement(START_DATE_TIME_FIELD.findElement(getDriver()), originalStart.replace("-03T", "-02T"));
             setFormElement(END_DATE_TIME_FIELD.findElement(getDriver()), originalEnd.replace("-03T", "-02T"));
@@ -197,6 +200,9 @@ public void testSchedule() throws IOException, CommandException
 
         assertProjectEventCounts(2, 0);
 
+        // The event chip time range is rendered via DateFormat (the patched parseTime path); verify it shows the real 8AM-5PM range, not a zeroed 00:00 - 00:00 as happened in colon-labelled timezones.
+        assertEquals("Event chip should show the 8AM-5PM time range", "08:00 - 17:00", getText(Locator.css(".activeProjectEvent .event-date")));
+
         doAndWaitForPageToLoad(() -> selectOptionByText(PROJECT_DROP_DOWN, PROJECT_2));
 
         scheduleInstrument(yearMonth + "-04", false);
diff --git a/webapp/TargetedMS/js/scheduleUtils.js b/webapp/TargetedMS/js/scheduleUtils.js
index 02588526f..7b4199c36 100644
--- a/webapp/TargetedMS/js/scheduleUtils.js
+++ b/webapp/TargetedMS/js/scheduleUtils.js
@@ -8,6 +8,18 @@
 (function(window) {
     const utils = {};
 
+    const pad = function(n) { return (n < 10 ? '0' : '') + n; };
+
+    // Date-only 'yyyy-MM-dd' wire form from local fields.
+    utils.toDateValue = function(date) {
+        return date.getFullYear() + '-' + pad(date.getMonth() + 1) + '-' + pad(date.getDate());
+    };
+
+    // Format a Date as datetime-local's fixed 'yyyy-MM-ddTHH:mm' wire form from local fields; avoids DateFormat, which zeroes the time in timezones whose label contains a colon (e.g. Honolulu).
+    utils.toDateTimeLocalValue = function(date) {
+        return utils.toDateValue(date) + 'T' + pad(date.getHours()) + ':' + pad(date.getMinutes());
+    };
+
     // Convert a CSS color string (named, rgb, hex) to standard 6-digit HEX color (#RRGGBB)
     utils.stringToColor = function(color) {
         if (!color) return '#888888';
diff --git a/webapp/TargetedMS/js/scheduler.js b/webapp/TargetedMS/js/scheduler.js
index f289542e2..622221018 100644
--- a/webapp/TargetedMS/js/scheduler.js
+++ b/webapp/TargetedMS/js/scheduler.js
@@ -88,10 +88,7 @@ $(function() {
                         let bgColor = e.event.extendedProps.project === project ? e.backgroundColor : 'gray';
                         const cl = e.event.extendedProps.project === project ? 'activeProjectEvent' : 'otherProjectEvent';
                         let textColor = ScheduleUtils.getContrastTextColor(ScheduleUtils.stringToColor(bgColor));
-                        let timeFormatString = LABKEY.container.formats.timeFormat;
-                        // Strip seconds and milliseconds
-                        timeFormatString = timeFormatString.replace(':ss', '').replace('.SSS', '');
-                        let dateStr = DateFormat.format.date(e.event.start, timeFormatString) + ' - ' + DateFormat.format.date(e.event.end, timeFormatString);
+                        let dateStr = ScheduleUtils.formatTimeRange(e.event.start, e.event.end);
                         let style = 'background-color: ' + LABKEY.Utils.encodeHtml(bgColor) + '; color: ' + LABKEY.Utils.encodeHtml(textColor) + ';' + 'width: 100%';
                         content += '<div class="' + LABKEY.Utils.encodeHtml(cl) + '" style="' + style + ';">'
                                 + '<div class="event-date">' + LABKEY.Utils.encodeHtml(dateStr) + '</div>'
@@ -396,8 +393,8 @@ $(function() {
             endDate.setDate(endDate.getDate() - 1);
         }
 
-        let startDateFormatted = DateFormat.format.date(startDate, LABKEY.container.formats.dateTimeFormat);
-        let endDateFormatted = DateFormat.format.date(endDate, LABKEY.container.formats.dateTimeFormat);
+        let startDateFormatted = ScheduleUtils.toDateTimeLocalValue(startDate);
+        let endDateFormatted = ScheduleUtils.toDateTimeLocalValue(endDate);
 
         // remove the old event log rows
         removeEventLog();
@@ -581,6 +578,13 @@ $(function() {
     });
 
     function fetchInstrumentCosts(instrumentId, startDate, endDate) {
+        // Normalize to Date: callers pass either Date objects (hover) or seconds-less datetime-local strings (post-save), which DateFormat can't parse as-is.
+        const start = new Date(startDate);
+        const end = new Date(endDate);
+        // Bail on degenerate input so the cost log never renders $NaN or garbage dates (mirrors calculateAndRenderCostPreview).
+        if (isNaN(start.getTime()) || isNaN(end.getTime()) || end <= start) {
+            return;
+        }
         LABKEY.Query.selectRows({
             schemaName: 'targetedms',
             queryName: 'instrumentRate',
@@ -595,7 +599,7 @@ $(function() {
                 }
                 let fee = data.rows[0].fee;
                 let rateType = data.rows[0].rateType;
-                let cost = fee * (Math.abs(new Date(endDate) - new Date(startDate))) / 1000 / 60 / 60;
+                let cost = fee * (Math.abs(end - start)) / 1000 / 60 / 60;
 
                 // query the rateType
                 LABKEY.Query.selectRows({
@@ -608,8 +612,8 @@ $(function() {
                     success: function (data) {
                         let setupFee = data.rows[0].setupFee;
 
-                        let startDateFormatted = DateFormat.format.date(startDate, LABKEY.container.formats.dateTimeFormat);
-                        let endDateFormatted = DateFormat.format.date(endDate, LABKEY.container.formats.dateTimeFormat);
+                        let startDateFormatted = DateFormat.format.date(start, LABKEY.container.formats.dateTimeFormat);
+                        let endDateFormatted = DateFormat.format.date(end, LABKEY.container.formats.dateTimeFormat);
 
                         let tableElt = document.getElementById('event-cost-table');
                         let rowElt = document.createElement('tr');