Yes time slot matters for actors in Pakistan as A-lister actors Only work for 8 pm dramas.
Usually actors who are new or not popular do 7pm and 9pm dramas. They are in B category. Once an actor becomes famous he stops working in these slots. There are many examples like Usama, Sehar, Ali Raza, Komal meer and Anmol Baloach who used to work in those slots but their one or two famous dramas made them lead for 8 pm slot. Now they are A-listers.
Lekin ARY ke 7pm ya 9pm dramo ki quality better hoti hai compare to other channels. ARY ke 7 ya 9pm ki quality Hum tv ke bahut se 8pm drama se bhi better hoti hai.
Also Ramadan dramas(not talking about Naqaab as it's not a ramadan drama) even though they come at 9pm or 7pm have same stature as 8pm dramas. Isliye A-lister ki list jo aapne di hai usme Laiba Khan ko bhi include kar sakte hai shayad. Her drama Sitaron se Aagay currently airing on express tv at 8pm & her Ramadan drama will air at 9pm on Geo. Her next drama with Mikaal could also be a 8pm drama & it could replace Daayan starring Mehwish & Ahsan.