I would keep messing with FP+ and see if you can get a later time to come up- in my experience, things change about every time you try it with their glitchy system. I had
MDE tell me there were no TT FP+ available for an entire day, then after I tried a few more times it gave me only evening times (I needed morning), and then after I kept messing with it it finally opened up just about any time in the morning I wanted. Maybe if you try it a few more times, it will show some better times for you.
I think it is going to be next to impossible to make both. If you want any kind of chance, you want to be at 1900 at least 20 minutes before 8, to try to be at the front of the group that will all be there for the 8:00 seating. I've heard of the place not opening exactly on time and of them not seating people with 8:00 a.m. adrs, until 8:10 or 8:15. The characters do not start coming through until 8:15 or 8:20, and it will take a while for them all to come through. You should expect that you probably will get out of the restaurant around 9, but there is a possibility it could even be as late as 9:30. The absolute earliest I think you could get out of 1900 would be 8:45 (unless you eat really fast and skip characters), but I think that is a long shot.
Also, we've stayed at the GF twice and both times the bus service was terrible, especially in the mornings. I don't think we've ever waited less than 20 minutes for a bus there. It is not the first stop on the bus route, and especially in the mornings, you will find that sometimes the buses fill up at the other resorts and they either drive through the GF and tell you they are full and the next bus will be along shortly, or skip the resort all together. They have an electronic board telling you when the next bus will be there, but in our experience, all we did was look at it and get excited that the next bus would be there in 7 minutes and then watch the time switch to later and later until we had waited 20 minutes to 30 minutes. We go in low crowd times too.
DHS is about 6 miles from GF- so it will take between 10 and 20 minutes for the bus to drive there depending on the morning traffic. Then you have to walk from the bus to the gate, go through bag check, get through the gate, and walk back to TSM.