16 how many hours can i work ?

So I'm 16 and I have a job interview for mcdonalds this upcoming Friday its my first job! And I get a government check I get a survivors benefit because my mom passed away of cancer and my sister was telling me if I worked too many hours they'll cut my check but she wxnts me to work like 20 hours and that's not enough I have to afford new clothing to keep getting my hair done and a cell phone bill and all I get for allowence is 50 dollars a month and its not helping at all so please tell me now many hours I can work and plus its summer time