Hi and Welcome to Fetcher! Happy to have you on board.
The syncing process is determined by the size of the Amazon account. For small accounts, it could take only a few hours (5-6) yet for medium to large accounts, it could take anywhere from a few hours up to 3-4 days.
This is because we don't pull all your data from Amazon at once and have to submit multiple API calls upon for each data requests based on Amazon's limits.
However, this is only when you first sign up and sync your account. After that, Amazon will share data with us much faster. Plus, we also place API calls every hour in order to have the most updated data for you.
Cheers to Increasing Profits!