We were some of the first into BOG for breakfast last Friday and were finished eating by 8:30 without trying to rush at all. We both got adult-size entrees and ate all the pastries too, but we aren't slow eaters.
I'd recommend being at MK gates no later than 7:45 and preordering if possible, so you can be in the first groups seated though. It was a madhouse in there by the time we were leaving. I don't think you'd have problems doing that with an 8:25 reservation; the sheet the person checking our reservations at the gate had listed any from 8-8:30 and I believe people were sent back as soon as they arrived regardless of reservation time...but we had an 8 am ADR, so I'm not positive.