Leave Islamabad, latest by 6:00.. so that you cross Mardan before rush hour.
As rightly pointed above you will have to hit Chitral same day as there is no worth staying place in between. You can take your first tea stop around Malakand/Chakdara... then late lunch break around Upper Dir (before tunnel), and then hit Chitral for dinner time.
Now that the tunnel is open to all traffic, you will save around 1.5 hour of your travel time.
Road is pretty good throughout, except for a 10 km patch before and after the tunnel.
In Chitral you can make a day trip to Bamburet (commonly known as Kelash valley). It takes around 3 hour one way from Chitral. It's a track and tests got nerves at times.
On the second day you can make a day trip to Garam chashma.
And then you can take off to shandur. Takes around 8 hours from Chitral. You can stay the night at PTDC Mastuj, last civilisation before Shandur top.