I ordered well after launch - on 9/17 - and I got tracking a few hours ago (around 1:30AM EST) via. an e-mail from UPS My Choice. Got the Sprint.com e-mail about an hour ago as well. Order was for 6S+ 128GB Gold. Tracking is similar to many others (as most are) and shows a 2 day air delivery scheduled for Friday, label generated/printed on 9/23.
Sprint seems fairly confident in their stock ability; as the order status for the 6S+ 128GB Gold (should be the same with Space Grey as well) originally said anything placed prior to 9/18 5PM CST would "do its best" to deliver by 9/25; they changed that to anything (at least for the 6S+ 128GB Gold) prior to 9/22 5PM CST would attempt delivery by 9/25 and then 2-5 days shipping time for new orders. That's pretty good, and I'm honestly surprised that they were able to pull through considering Apple.com was 3-4 weeks. I usually go through Apple directly but I didn't order right at launch and I noticed that Sprint's website was showing good stock online, and it seemed to have turned out as promised.
Also, UPS ships fairly fast from their Louisville, KY location as it is their headquarters/world hub, so I wouldn't worry too much about the lack of updates on the tracking page as it pretty much goes direct to many destinations from the hub and the 'cutoff' times are very late as it's usually the main outgoing point to your closest city.