From sign-up to your first sale.
From sign-up to your first sale and refund, in five missions. About an hour in all, and you can stop between missions.
Connect your own card processor so the register can charge cards. About ten minutes, and you can start on cash and come back.
Bring in what you sell, a spreadsheet for many, by hand for a few. About fifteen minutes.
Sell something real, print the receipt, then refund it, so you have done both before a customer is waiting. About ten minutes.