Glossary
StartBoundary
The trigger element giving the date and time from which a scheduled task trigger is active, usually stored as local time with no UTC offset.
StartBoundary is part of every trigger type and is required for time and calendar triggers. Microsoft's API documents the format YYYY-MM-DDTHH:MM:SS(+-)HH:MM (Trigger.StartBoundary), but tasks created in the console or with schtasks usually omit the offset, so the value is the machine's local time.
It marks when a trigger becomes active, not when the task ran; run times come from TaskCache DynamicInfo and event logs. Convert it with the machine's UTC offset before comparing with UTC evidence. See task XML anatomy.