How often are contact records queried to see if a "wait until" condition is met?

I’m trying to trigger next steps based on Custom Contact fields that are updated via API from my own database - specifically purchase data. So if I have someone in a sequence and they hit a “wait until product x is purchased” with no expiration, and my API updates that field once per day, will it trigger the next step immediately upon update? 5 minutes after? 1 hour…