Saturday was my 180 day and I too had issues online... here's what I experienced/learned.
Online several times after midnight/before 7am and could not make reservations due to no availability and/or system acting wonky
You MUST log in to your
MDE before trying to make your 180+10 ADR's or it will not let you pick a date on the calender after your check in date...wish the system prompted that because it was driving me crazy!
Called at 7:10am - extensive wait time - finally hung up after nearly an hour and figured I'd try later on when I had time to concentrate on it instead of while in the car.
Later that afternoon I logged in online again and was able to make ALL my ADR's with the exception of Crystal Palace before MK opens on our 1st park day and BOG - for 11 days I didn't think 2 ADR's were an issue.
Since Saturday I have repeatedly looked for those 2 ADR's (online only) as my computer is pretty much on 24/7 and it takes only a couple minutes to check and got Crystal Palace last night (so someone canceled and I was able to get it

)
I'm figuring on continuing to try to get BOG but from the reviews I've read and the "how to score" a BOG reservation, we'll just do QS there if we don't get the TS reservation. We're going with the FD (again) and I'm not going to let ADR's ruin the trip... if we get them great, but we'll figure out somewhere to eat if not.
If you make an ADR but it was not for the "ideal" time... keep checking availabiliy online for that ADR, IF the time you really want becomes available, click and reserve the new reservation. The system prompted me that there was another reservation for that day/time frame and did I want to change my reservation. It will hold your original reservation until you confirm the new one. This way you can flex your reservations w/o losing 1 first.
Lastly, a CM told me that the best opportunity to get those hard to get ADR's is to try at your 45 day mark as that is when the final payment is due for trips and many people end up cancelling their trips when they realize they really couldn't afford it.