Because of the volume of Transactions stored in the transaction lines table we have implemented a period selection interface for Transaction Headers, Transaction Lines and Job Actuals. This selects just the data for the periods chosen and is much faster to synchronize.
When ExSync is synchronising the data, It requires you to select the period before connecting to the database.
This is because Job Actuals and Transaction lines are put in a temporary database before syncing, which means that every time you select the period, the temporary table needs to be emptied.
These steps should always be completed before a sync, and are covered in the install guide here