Upgrade time at a Super Regional will be an average of the upgrade times of each of its component parts.
Its a simple mathematical formula:
Upgrade time U = Attrition A + Growth G.
So (Uru + Uev + Uoo)/3 = Usuper-regional
The quick upgrade of a Colgan is based on their high attrition - both FO's who don't wait for upgrade and bail at first opportunity, and CA's who survive their 1000 TPIC and then move. At GoJets its based on massive (relative) growth. Double your airframes every year, and you've got a 1 year upgrade, even with zero attrition. All three carriers here are well established and unlikely to have large scale internal growth(which is why OO is buying other carriers - to show year over year growth to the stock market).
Eagle, Horizon and Comair have had long upgrades because of low attrition and low growth - both possibly because of their good contracts! (Contented pilots don't go looking for a better gigs.)
Its possible that attrition will slow at the new company, if the average quality of life is raised, and fewer pilots desire to leave. Or overall attrition might increase if the average pilot finds the new group less pleasant than the previous regime.
Likewise if attrition decreases due to lowered major hiring, it will affect a single large group in the same proportion as it would three smaller groups.
The junior CA at RU and EV are only a couple months apart, but both have a year and a half on the junior RJ CA at OO, and over two years on the junior Bro CA. So, obviously there will be some settling, but nothing dramatic.