I spent time just watching the queue timers for each mode.
Even changed Regions to see if that made a difference.
Here's the results I got:

Casual
3 minutes - Arena, Joust
4 Minutes - Conquest, Assault
5 Minutes - Clash
6 minutes - MotD
12 minutes - Siege

Ranked
10 Minutes - Joust
12 Minutes - Conquest, Duel

I would have thought timers would be modified by people online, certain regions have more players and certain time of the day also.