The way I have seen it best done is "preemptively", [@ELGainsborough]. Initiative rolled at the start, prior to an encounter or event, then right after for the next so that there is no delay or waiting. It also works in some part to determine which character is doing what and or slightly distracted. 

Not as intended for Third Edition, but it works well enough and is standardized that it doesn't betray if something is or isn't combat.