It's locked during full the processing of all 500 items. If the collection time expires during processing, then another node has the ability to "steal" the lock and those 500 items get double-processed. In this case the processing is subject to race-conditions.

1 minute is anticipated to be more than enough for the processing of 500 items (if not, I think we might have bigger problems to deal with). However, telemetry is in place to evaluate this and adjust configuration as necessary.