All sync requests are sent to a queue after being issued. Depending on the length of the queue, it could take up to half an hour for a quick sync to be performed. Normally, however, it should only take about 5-10 minutes for the sync to start, if not immediately.
Full syncs are normally scheduled out of normal working hours as they require a much larger transfer of data. Please allow up to 1 day for a full sync request to be performed.