When the integration e.g. between Jira and ServiceNow is created, its first run will ask both sides to provide items that changed after the timestamp equal to current time stamp (lets call it TIMESTAMP 1). Another run of that integration which will happen after a specified delay (in seconds), will ask for items that were changed after TIMESTAMP 1. Start of that second run is captured (lets call it TIMESTAMP 2). Next run will ask for items that changed after TIMESTAMP 2, and start of that third run will be captured as well. That cycle of changes fetching will be repeated until integration is disabled or deleted.