diff --git a/Core/Resgrid.Model/Helpers/TimeConverterHelper.cs b/Core/Resgrid.Model/Helpers/TimeConverterHelper.cs
index 56bc3e232..bd47b5a70 100644
--- a/Core/Resgrid.Model/Helpers/TimeConverterHelper.cs
+++ b/Core/Resgrid.Model/Helpers/TimeConverterHelper.cs
@@ -12,28 +12,26 @@ public static class TimeConverterHelper
 	{
 		public static DateTime TimeConverter(this DateTime timestamp, Department department)
 		{
-			DateTime newTime = timestamp;
-			TimeZoneInfo timeZoneInfo = null;
-
 			// If department is null we gotta just bail
 			if (department == null)
 				return timestamp;
 
 			try
 			{
+				string timeZone = "Pacific Standard Time"; // Default to Pacific as it's better then UTC
+
 				if (!String.IsNullOrEmpty(department.TimeZone))
-					timeZoneInfo =
-						TZConvert.GetTimeZoneInfo(
-							DateTimeHelpers.ConvertTimeZoneString(department
-								.TimeZone)); // TimeZoneInfo.FindSystemTimeZoneById(DateTimeHelpers.ConvertTimeZoneString(department.TimeZone));
-				else
-					timeZoneInfo = TZConvert.GetTimeZoneInfo("Pacific Standard Time");// TimeZoneInfo.FindSystemTimeZoneById("Pacific Standard Time");	// Default to Pacific as it's better then UTC
+					timeZone = department.TimeZone;
 
-				if (timeZoneInfo != null)
-				{
-					newTime = TimeZoneInfo.ConvertTimeFromUtc(timestamp, timeZoneInfo);
-				}
-				return newTime;
+				// Resolve via NodaTime's embedded IANA database instead of TimeZoneInfo /
+				// TZConvert.GetTimeZoneInfo. The hardened (DHI) container ships without ICU and
+				// runs in globalization-invariant mode, where TimeZoneInfo cannot map a Windows
+				// zone id and throws TimeZoneNotFoundException. NodaTime carries its own tzdb and
+				// needs neither ICU nor the OS /usr/share/zoneinfo files. Mirrors TimeConverterToString.
+				var ianaTz = TZConvert.WindowsToIana(DateTimeHelpers.ConvertTimeZoneString(timeZone));
+
+				var instant = Instant.FromDateTimeUtc(DateTime.SpecifyKind(timestamp, DateTimeKind.Utc));
+				return instant.InZone(DateTimeZoneProviders.Tzdb[ianaTz]).ToDateTimeUnspecified();
 			}
 			catch (Exception ex)
 			{
@@ -101,21 +99,21 @@ public static string FormatForDepartment(this DateTime timestamp, Department dep
 
 		public static TimeSpan GetOffsetForDepartment(Department department)
 		{
-			TimeZoneInfo timeZoneInfo = null;
 			TimeSpan timeSpan;
 
 			try
 			{
+				string timeZone = "Pacific Standard Time"; // Default to Pacific as it's better then UTC
+
 				if (!String.IsNullOrEmpty(department.TimeZone))
-					timeZoneInfo = TimeZoneInfo.FindSystemTimeZoneById(DateTimeHelpers.ConvertTimeZoneString(department.TimeZone));
-				else
-					timeZoneInfo = TimeZoneInfo.FindSystemTimeZoneById(DateTimeHelpers.WindowsToIana("Pacific Standard Time"));    // Default to Pacific as it's better then UTC
+					timeZone = department.TimeZone;
 
-				timeSpan = timeZoneInfo.BaseUtcOffset;
-				var currentDateTime = DateTime.UtcNow.TimeConverter(department);
+				// NodaTime tzdb (no ICU / OS tzdata dependency, unlike TimeZoneInfo). GetUtcOffset
+				// already folds the active DST rule into the returned offset for the given instant.
+				var ianaTz = TZConvert.WindowsToIana(DateTimeHelpers.ConvertTimeZoneString(timeZone));
+				var instant = Instant.FromDateTimeUtc(DateTime.SpecifyKind(DateTime.UtcNow, DateTimeKind.Utc));
 
-				if (timeZoneInfo.GetAdjustmentRules() != null && timeZoneInfo.GetAdjustmentRules().Any())
-					timeSpan = timeZoneInfo.GetAdjustmentRules().Where(timeZoneAdjustment => timeZoneAdjustment.DateStart <= currentDateTime && timeZoneAdjustment.DateEnd >= currentDateTime).Aggregate(timeSpan, (current, timeZoneAdjustment) => current + timeZoneAdjustment.DaylightDelta);
+				timeSpan = DateTimeZoneProviders.Tzdb[ianaTz].GetUtcOffset(instant).ToTimeSpan();
 			}
 			catch (Exception ex)
 			{
diff --git a/Core/Resgrid.Services/CallEmailTemplates/ParklandCounty2Template.cs b/Core/Resgrid.Services/CallEmailTemplates/ParklandCounty2Template.cs
index d0204a37a..8c3f35434 100644
--- a/Core/Resgrid.Services/CallEmailTemplates/ParklandCounty2Template.cs
+++ b/Core/Resgrid.Services/CallEmailTemplates/ParklandCounty2Template.cs
@@ -4,9 +4,11 @@
 using System.Linq;
 using System.Text.RegularExpressions;
 using System.Threading.Tasks;
+using NodaTime;
 using Resgrid.Model;
 using Resgrid.Model.Identity;
 using Resgrid.Model.Providers;
+using TimeZoneConverter;
 
 namespace Resgrid.Services.CallEmailTemplates
 {
@@ -51,8 +53,17 @@ public async Task<Call> GenerateCall(CallEmail email, string managingUser, List<
 						var priorityString = c.Name.Substring(0, c.Name.IndexOf(char.Parse("-"))).Trim();
 						priorityChar = Regex.Replace(priorityString, @"\d", "").Trim();
 
-						TimeZoneInfo timeZone = TimeZoneInfo.FindSystemTimeZoneById(department.TimeZone);
-						callTimeUtc = new DateTimeOffset(DateTime.Parse(data[0].Replace("Date:", "").Trim()), timeZone.BaseUtcOffset).UtcDateTime;
+						// NodaTime tzdb (no ICU / OS tzdata) — DHI runs in globalization-invariant mode where
+						// TimeZoneInfo.FindSystemTimeZoneById can't resolve a Windows zone id. InZoneLeniently is
+						// DST-aware (the prior BaseUtcOffset ignored DST, drifting an hour for ~8 months/year) and never throws.
+						// Default to Pacific (matches TimeConverterHelper) so WindowsToIana never receives a null/blank id
+						// and throws InvalidTimeZoneException, which would silently downgrade callTimeUtc to processing-time UTC.
+						var windowsTz = String.IsNullOrWhiteSpace(department.TimeZone)
+							? "Pacific Standard Time"
+							: department.TimeZone;
+						var ianaTz = TZConvert.WindowsToIana(windowsTz);
+						var localCallTime = LocalDateTime.FromDateTime(DateTime.Parse(data[0].Replace("Date:", "").Trim()));
+						callTimeUtc = localCallTime.InZoneLeniently(DateTimeZoneProviders.Tzdb[ianaTz]).ToDateTimeUtc();
 
 						is2ndPage = c.Notes.Contains("WCT2ndPage");
 
diff --git a/Core/Resgrid.Services/WorkflowTemplateContextBuilder.cs b/Core/Resgrid.Services/WorkflowTemplateContextBuilder.cs
index 0963ff8d3..ff554fad6 100644
--- a/Core/Resgrid.Services/WorkflowTemplateContextBuilder.cs
+++ b/Core/Resgrid.Services/WorkflowTemplateContextBuilder.cs
@@ -4,6 +4,7 @@
 using System.Threading;
 using System.Threading.Tasks;
 using Newtonsoft.Json;
+using Resgrid.Framework;
 using Resgrid.Model;
 using Resgrid.Model.Events;
 using Resgrid.Model.Providers;
@@ -357,10 +358,12 @@ private static void AddCommonTimestampVariables(ScriptObject obj, string timeZon
 			DateTime deptNow;
 			try
 			{
-				var tz = !string.IsNullOrWhiteSpace(timeZoneId)
-					? TimeZoneInfo.FindSystemTimeZoneById(timeZoneId)
-					: TimeZoneInfo.Utc;
-				deptNow = TimeZoneInfo.ConvertTimeFromUtc(utcNow, tz);
+				// NodaTime tzdb (no ICU / OS tzdata). DHI runs in globalization-invariant mode where
+				// TimeZoneInfo.FindSystemTimeZoneById can't map a Windows zone id (TimeZoneNotFoundException).
+				// DateTimeHelpers.GetLocalDateTime resolves UTC -> department-local via the embedded tzdb.
+				deptNow = string.IsNullOrWhiteSpace(timeZoneId)
+					? utcNow
+					: DateTimeHelpers.GetLocalDateTime(utcNow, timeZoneId);
 			}
 			catch
 			{