it definitely depends...most UC schools do a quick #s screen via a computer algorithm (gpa & mcat)...if you pass that screen, your secondary comes almost immediately (1-2 weeks). if not, your app goes into a huge pile that needs to be reviewed by hand to see which candidates with less than perfect #s still deserve a shot. that process can take much longer, anywhere up to 4 months later...
as a hypothetical:
Primaries rec'd: ~4000
Secondaries sent out in total: ~2000
Automatic comp algorithm then sent: ~1500
Hand-reviewed then sent: ~500
best advice i can give: even if you don't think you have the #s for a UC school, apply anyway. make ur app the strongest you can because in the end, it is still looked at before you are rejected. stay positive and don't get caught up in the numbers game. at the end of the day, doctors have to be good ppl as a whole and a few digits on a piece of paper mean nothing.