Assuming direct from Glasgow or Edinburgh to Budapest, usually just under 3 hours. It could be longer if you were going from Northern Scotland to Eastern Hungary (Budapest, the capital, is in the west of Hungary).

Unfortunately, I don't think you can get a direct flight (see example list of flights on Yahoo travel). In which case you're looking at a minimum of 4 hours travel time each way, and that's if you only have one stop-over to contend with.