I can give it a shot, although not being a Compass or Endeavor pilot I may be off on a few details.

The flow-through hires are coming from Compass, which had a flow agreement with Northwest prior to their merger with Delta. After the DL/NW merger the Compass flow was set to eventually end, but not until all the covered pilots have flowed to Delta. We are nearing the end of that now and it should conclude in November I believe. Up until then they'll have approximately 20 spots per month.

SSP hires are coming from Endeavor (formerly Pinnacle/Mesaba/Colgan), which was acquired by Delta out of bankruptcy. The Endeavor pilot contract was gutted in this deal, but a trade off was a Streamlined Selection Process (SSP) for interviews at Delta. They have a 1-day interview and after they receive a CJO they are metered from Endeavor at a certain rate, seemingly 12-15 or so per month. Originally this was only available to Endeavor Captains, but was extended to some F/Os and very recently to more F/Os. Most of the SSP folks interviewing now won't see class until late 2016 or beyond due to the metered hire rate. The latest extension of the program will require Endeavor F/Os to be Captains there for 2 years before getting a class date with Delta, so this program is very much a pilot retention measure for the wholly owned regional airline.

The rest of us are off-the-street (OTS) applicants, and we get class spots after the entitlement quotas are met. Smaller class sizes mean less spots for us, but that situation should improve after the Compass flow ends. Hopefully September class sizes are larger and things get moving again.

I'm an April 23rd CJO as well and I think late September is a good guess.