I wonder if the issue is more the time of the day.

Last Thursday I decided to go experience on my level 15 Rogue. Queued for the two level 15 Guildhests and 15 minutes later they were both done. Queued for the Guildhest roullette and it popped in less than 5 minutes. Was level 16 and decided to queue for Sastasha, average timer said over than 30 minutes, it popped after around 20 minutes. Did this all after 11 p.m. GMT and ended up with a level 18 Rogue.

Waiting for the DF to pop is always annoying, but that's why I always go do other stuff while waiting (like Beastmen quests and GC deliveries).