You can manage Hunza Karimabad - Khunjarab pass - Hunza Karimabad the same day with the following plan:
Karimabad to Attabad Lake = 40 minutes drive
Attabad Passanger Boat Journey = 35 minutes
From Attabad to Khunjarab Pass= 4 Hours (including lunch, prayer and picture stop)
From Khunjrab Pass to Hunza Karimabad = 4.5 hours (return journey is much faster)
I did this trip in one day because with the family it's not easy to take luggage across the boat and secondly, our driver was afraid of taking the car across the lake so he had to wait for us on the lake until we return.
We had rented another car for the return trip after the lake till khunjrab pass & he was a local driver so was over speeding but fine by me if it cuts down on time. Once you reach other side of the road you will be approached by different drivers and you can negotiate the rates with them,
On average you need 11-12 hours for a return trip from Hunza Karimabad to Khunjrab pass but you should leave at 6am.
Hopfully this will help.
