Re: Karachi to Gilgit
The train ride from Karachi to Rawalpindi takes around 25-30 hours depending on what train you are choosing.
You can go to Pakistan Railway and then “Plan Your Journey”.. That will tell you which train will take least time from Karachi to Rawalpindi. Getting late is also very common for Pakistani trains so always prepare your mind for a late arrival of 2-3 hours.
I think visiting Naran valley would be a better option for you this time because you have only 10 days in Pakistan out of which few will be reserved for your main reason of coming (like meeting family or official work). So, in real you have like 6-7 days for the trip.
Rawalpindi to Gilgit is almost 26 hours way (i.e. because of repairing of Karakoram Highway. All of it after Besham is not paved and the whole way is bumpy. Road closures are also observed because of work in progress). And from Gilgit to Hunza it takes 3-4 hours more.
Naran valley is about 10-12 hours from Rawalpindi and you can reach there by PTDC bus which goes daily at 9 AM from Flashman Hotel. Other options are available too if you miss the bus. (i.e. going to Mansehra from Rawalpindi on Daewoo Bus Service and from there you can catch a van or a bus to Naran).
Naran valley also has many attractions like Lake Saif Ul Maluk, Aansu Lake, Lalazar, Lulupatsar Lake, Jalkhad etc.
Our Northern Areas are also very beautiful and 6-7 days are way too less to explore the Northern Areas. I went there but I had few days + tight budget so I wasn’t able to explore the beauty of our Northern Areas at full extent. May be next year I’ll go for more detailed tour.
If you have anymore questions, feel free to ask 