DateTimeDiff returning negative values in Architect expression

Running into a weird edge case with DateTimeDiff in a Data Action. I’m trying to flag calls that happened more than 24 hours ago, but the diff returns negative numbers when comparing now() to a past timestamp, breaking my > 86400 check.

Here’s the expression:

DateTimeDiff(now(), GetDateTime("interaction.timestamp"), "seconds")

Is there a known bug with the order of arguments or am I just missing a wrapper function?