How often do you let your preschooler play on Iphone/Ipad?

My daughter is 7 years old and is only allowed to play for an hour during dinner, before dinner time and after she has completed all her work. I know gadgets are unhealthy but the games she's playing aren't really those typical "mindless" games so I don't mind. Sometimes she gets bored quickly and wouldn't finish up her hour so this arrangement works for me best.