This is an age old question that many people here wonder themselves. If this is an industry you want to get into, you will find out that it is very unpredictable. Point being, upgrade times to CA vary from airline to airline and can change at any minute. I know that's a vague answer but that is the reality. Right now if you were hired, there are places that advertise upgrade times at anything from around 2 to 6 years. And that's a real rough estimate. Again, that could all change tomorrow. Try searching around the forum, do as much research as you can; you may find that upgrade times might not be the most important part of picking an airline also, some people go for Quality of Life (pay, living in base, etc etc) over upgrading.

Hope that helps, good luck with your search.