Expression syntax for comparing dates in Architect — DateTimeDiff vs GetDayOfWeek

Quick question about Architect expression syntax.

I’m trying to validate a date range in a Data Action, but DateTimeDiff returns an error when passed raw ISO strings from the payload. Should I be converting these to epoch timestamps first, or is there a specific format requirement for the GetDayOfWeek function that I’m missing?

ERROR: Invalid argument type for DateTimeDiff. Expected long, received string.