WAS
Good to see you could avail that many leaves. But since I only have four days so I won't be able to travel to Gilgit side. I would rather travel to Swat/Naran to spend more time on actual trekking.
Based on your days, you can do Fairy Meadows, Hunza, Khunjerab trip, or Skardu, Shigar, Deosai.
Mostly 18 days are used for some longer trekking trip.