Celerity
 

Level 39 enchanter spell
Celerity reads
Spell Effect: Grants your target quickened movement, increasing their attack speed for 0:16:00.

Currently it only lasts 13 minutes when cast.

I apologize if this has already been addressed.

This is likely one of those spells that increases as you level up.

I've noticed this spell expiring when the mouse over duration has 2-3 minutes left. I think this is the problem he is talking about.

actually my level 40 enchanter cast Celerity on himself and it only shows a time of 13 minutes

I have 16 minutes at level 50.

Make sure your spell files are up to date?

Lasts 16 minutes for me at 50.