μήπως (= whether/ if) is used only in questions in direct or indirect speech.
Μήπως έχεις ώρα; = Do you have the time? (direct question)
Με ρωτάει μήπως έχω ώρα. = He asks me if I have the time. (indirect question)
ίσως (= perhaps / maybe) is used in statements.
Ίσως έρθω αύριο το πρωί. (= Perhaps I come tomorrow morning)