Well I believe that would be at least 2pm.
You need at least 8 hours to reach Thall village from islamabad.
So thats 10pm but in dark it might take a little more as the road is very bad at the end.
Hotels are readily available in Thall but at 10pm, you will have difficulties in finding a hotel there.
In my opinion, in your situation of friends trip, its better to stay inside Kumrat rather than Thall. So better to leave late night and reach early morning in Thall and take a jeep from there to Kumrat. Jeep will cost around 6-7k I think for waterfall and then till Kala chashma. For Do-Janga, they might ask 10k. (Thats the round trip.
In your case, you should get a jeep to leave you inside the valley. You can find many hotels there. Kumrat Maskan is best I think but a little expensive. You can find tents as well, that would be cheap and good adventure as well.
Go at least till Kala Chashma. Then you can also have some trekking on some smaller tracks with info from locals (on second day).
On sunday, you must leave Thall village at about 3pm so that you can reach Sheringal before sunset. After that its a smooth road.
