The 1500 hours for upgrade is the minimum that the FAA requires for a Part 135 PIC and since PlaneSense was hiring pilots with about 700 hours (sim time doesn't count even Level D) it was taking a little over a year to get the 1500 hours. Post Covid I'm not sure how the upgrades will go as it will depend on how many are leaving for the Regionals and if they don't mind being fat on Captains.
As for the jets recently the new upgrades had 4 years seniority however the upgrades to the jets are being delayed as they announced that they are deferring buying new PC-24s due to the current situation, while they are still trying to sell the Nextants, so that will increase the time needed to go into the jet.