Shouldn't it be के बाद and not just बाद?
both are fine
Each time these sentences say something " will happen later" I'm guessing it means "in so many hours time"
It looks like an awkward translation into English.
Or does it really mean "later" ?
बाद is later and घंटे are hours. Hope that resolves your doubt!
Shouldn't खेलेंगी be plural since लड़कियाँ is plural?
खेलेंगी is plural singular of it will be खेलेगी. The singular does not have the dot while the plural does which additionally also slightly changes the pronunciation. Hope that helps!