Assuming you are applying to majors also. If not, do that as well.

500 mil hours (in same cat/class) can be credited to the FAA requirement of 1000 hours of part 121 SIC time required to upgrade (so you can upgrade at 500 hours if your seniority can hold it). I don't know what Atlanta based regionals have a quick upgrade time, if any. FYI it took me about 10 months to get 500 hours at Mesa from hire date. Would have been a little quicker if I stayed in a junior base and got a line quickly. Upgrade doesn't matter much in my opinion for you though, as you have mil heavy PIC time. You probably won't be at the regionals long.