Staff Scheduling App?

Hi I met my partners extended family this xmas. And one of them actually runs a jewellery store. Quite profitable business because they are making 300% profit on each sale. Their suppliers, invoicing, stock etc. is all set. One thing the business struggles with is staff scheduling. Business only has 9 staff, but jewellers has to operate almost 12 hours a day. So I looked into the details and found out that currently the scheduling is done on a spreadsheet. Now that lights up my founders brain. As its a saying on product hunt that if a business is doing something on a spreadsheet consider it an opportunity. So I would like to go on and build a staff management app. But before doing that I would like to ask PH, what features would you like to have in a staff scheduling app??