1. If you arrive on-time at 8:15, you should be at Pop by 9:45ish. You might be able to get into your room. If so, that will take you about 30 mins to check it out, freshen up and get back to the bus stop. If not, you can drop your carry on bags with Luggage Assistance and head to Epcot. I wouldn't make an FP+ for earlier than noon. That will allow you to be more relaxed.
2. For a 5:00pm departure flight, DME will give you a p/u time of about 2ish..give or take 15 mins either way. You don't schedule it, they will tell you what time. You need to be at that bus stop at least 15 mins prior to the p/u time they give you, bags in hand, ready to go. The time given is NOT the time to be leaving the gift shop or the rest room and ambling over to the stop!!! You could very well be left behind. So, you need to be ready to leave by 1:30ish. IF you decide to go to a park for the morning, you need to be leaving that park by noon. And don't forget to check your bags with RAC that morning.