Mac Events/Reminders
If you are using Mac Events and Reminders, Informant gets notified whenever OS X syncs and we update our views within the next few seconds (sometimes we may get dozens of notifications and we wait for 1 second after the last notification to ensure we don't flash the screen multiple times in quick succession).
Informant Synced Events/Tasks
If you are allowing Informant to handle the syncing of your items via Google, Toodledo, or Informant Sync - then as you make changes in Desktop Informant the changes are immediately synced up to the server. However if you make changes outside of Informant, then by default Desktop Informant will perform a sync every 15 minutes.
You can manually force Informant to perform a full sync by hitting CMD-R or choosing Refresh Sync Accounts from the File menu.