Apply as soon as you meet all of the minimum requirements. They are very firm on the minimums and won't budge on the multi or instrument time either. I've been at SkyWest almost six years and don't know if things have changed but plenty of people get hired without an internal recommendation (if not most).
As far as classes/staffing go we are currently very heavy on reserves in SLC and DEN. Additionally, there may be some more cutbacks on the Delta side in January. I'm not sure about newhire classes, but upgrade/transition classes have been put off until at least March.