Rarity is the prime factor. Then level, and finally different types (at least my heavy tanks of the same tier and approx. level take longer than the lights and mediums). I know my level 10 5star medium takes a bit more than an hour, and the level 12 4star medium takes under 45 minutes. I believe my level 12 or 13 3star heavy also takes around 40 minutes when it dies. My level 10 4 star destroyer, I think takes less time, but I don't know for sure. I'll have to actually LOOK at all the repair times the next time I wipe, instead of just noticing which is the longest delay, and deciding if I really want to bring that tank along to the next fight.
Yes, I can easily see a level 20-25 5star taking 2 hours to repair. As for waiting vs using resources, that's a play style choice. With a reserve of 50+ tanks, you could swap out every tank in your army. Especially since I would hope that there are some maps where you have a much easier time if you vary the tanks you bring.