Architect Expression: DateTimeDiff vs GetDayOfWeek logic error

Running into a weird issue with date logic in a Architect flow. Need to filter out calls that land on weekends before routing to a specific queue. Tried using the built-in expression DateTimeDiff(Now, CallStart, Day) but the result seems off when crossing time zones. The flow is set to US/Pacific, but the CallStart timestamp comes in as UTC. The math doesn’t line up.

Tried switching to GetDayOfWeek(CallStart) to check if it’s 1 (Sunday) or 7 (Saturday). It works fine for local times, but fails for late night PST calls that are already Monday UTC. The expression returns 2 (Monday) even though it’s Sunday night for the caller.

Here is the current expression setup:

IF(GetDayOfWeek(CallStart) == 1 OR GetDayOfWeek(CallStart) == 7, "Weekend Queue", "Weekday Queue")

Is there a way to force the GetDayOfWeek function to respect the flow’s timezone setting instead of the raw UTC value? Or should I be using DateTimeDiff with a specific offset calculation? The docs are vague on timezone handling for these specific functions.