As has been stated before both here and on reddit, the game attempts to match pre-mades with pre-mades to reduce the amount of pub-stomping, but then after a period of time it will allow pre-mades to be matched up with the solo queue. There is a hidden ELO score which it tries to make the average for both teams to be equal. Actual numbers, as well as what factors into this ELO score have not been published or stated. The player base has realized that brand-new players are given a significantly higher ELO than a new persons skill level resulting in players < lvl5 being thrown into a group where everyone else is lvl 25+ (on a regular basis).
On average here are my queue times since I started tracking this info:
Solo - 2:36 (111 data points)
Duo - 2:41 (32 data points)
Trio - 4:11 (only 3 data points)
Quad - 6:13 (only 1 data point)
Full - 3:21 (only 6 data points)
For a closed beta I think these wait times are appropriate, and for the final release/open beta, really only my 3 and 4 man queue times need to come down to sub 5 minutes. Most MOBAs and FPS ladder rankings have wait times of < 5 minutes per match and do an excellent job of matching skill levels of players in and out of groups (presuming the player has played 20-30 games). For now deal with the wait times. when the game hits open beta and/or gets released then is an appropriate time to worry about queue times for pre-made groups.
"Sometimes you have fun, sometimes the fun has you."