Honestly - when I have numbers like that, all I can say is that your mileage may vary on game time. I do believe game time shortens over multiple plays. But that belief is just based on my own personal experience, and then the experience of the other playtesters I've seen around me.
IMO, the real questions with regards to time-limits are:
1) Are there legitimate strategies that are centered around dragging games out for a very long time? If so, do the developers believe that such strategies should be curtailed? (analogous to 13-hour MTG decks, "Hide the Farm" in RTS games, "keep-away" strategies in fighting games)
2) Are there legitimate situations ("true stalemates") in which two competitive players could play for an infinite amount of time?
The second question has a pretty obvious answer: Yes. If both players have one Mage Wand with Heal, neither player has a Dissolve, and neither player has enough creatures or attack spells to out-DPS Heal, then you have a true stalemate. Like a Chess stalemate, it is mathematically impossible for either player to win unless the other player deliberately performs a wrong move.
I have to think that any competitive/organized version of Mage Wars would need some kind of time limit and tie-breaking rules. It may even have to deal with stalemates in some arbitrary way.
There's plenty of ways to deal with "ties":
- you can award a true tie where neither player gets the win
- you can award a win based on an arbitrary metric like "total damage taken" or "highest health remaining"
- you can award a win based on a completely random coinflip
- you can award wins based on pseudo-random "shoot-out" rounds like in soccer
- you can award wins based on "overtime" gameplay with significantly altered rules ("sudden death", "NFL playoff overtime rules")
- Or you can refuse to deal with ties, like tennis and baseball, where there is no theoretical reason why a game couldn't last for 1 year.