There are two different types of syncs that happen between Re-Leased and QuickBooks Online.
Automatic Sync
Automatic sync happens every five minutes.
This will synchronise all data between QuickBooks Online and Re-Leased.
Manual Sync
You can also force a manual sync under Settings > Manage Add-ons and integrations > QuickBooks Online add on. You can force all data to be synchronised using the sync all data button.