PRG is a very connection-friendly airport. IMHO it's the best place to connect in Europe (VIE coming a close second). 0835 is not only safe, but it ensures you'll have plenty of time at the airport for a coffee and sandwich, after which you'll even start getting bored. I've made a 35 min connection and quite a few that were under an hour. In my last 40 or so segments on OK, I have experienced one delay of about 2 hours so I would say it's extremely unlikely that you will have any such problems.
Do bear in mind that the PRG-BUD route is codeshared between OK and MA (check that you are able to get miles for a MA-operated flt, you certainly can get OK miles but not sure about anyone else's) and, in case you dislike turboprops, that some of the OK-operated flights feature ATRs (peak-time OK flights are on the 735, while MA use Fokkers).