Just my two cents...
Speaking only for the federal side of the wilderness:
Devils Slide is the only trailhead with a quota, so if you must enter there, be aware that on busy weekends/holidays you may be out of luck. Otherwise any other trail head (South Ridge, Seven Pines, Marion etc..) there is no trail quota. The same idea applies to which back country area you plan on camping in. If its a popular one, they may bump you to you second or third option. Its never happened to me, but I like to be where others aren't
As far as hiking without a permit...my understanding is that in most situations the ranger(volunteer) will read you the riot act, take down your pertinent info and send you on your way with an extra load of guilt on your back. But I doubt you'll do time or even be turned away.
Lastly, on the permit turn around...I've always faxed mine in to the San Jacinto station and usually have it back in about 3 business day.