What happens during the initial sync?
PieSync will first scan all your contacts in both applications even if you only choose to sync a subset. This initial scan is necessary to avoid duplicates. After this scan, the synchronization will start! If you have a lot of contacts, this can take a bit longer.
Once the initial sync is done and the connection is active, we scan every 5 minutes for updates and creates in your contact databases. Of course, if a previous sync or scan is still ongoing, we will first wait for that to finish.