They released new Mac mini's last year just a few weeks after WWDC together with Lion.
July 20. Which was 6 weeks after WWDC.
Although, the 2010 mini's came out June 15, which was 1 week after WWDC. So who knows.
Simultaneous with ML seems like the better bet than announcing "it's Tuesday" though, especially if we're also watching for Nvidia 680m's.