I know from personal experience that the Ivory Gates scenario can be beaten in about two and a half months, and the time limit for the Elven Lands scenario is six months (and I assume that it will take about that long to complete the scenario).

Are there enough elves in the Epic Battle to justify spending five months or so in the Elven Lands rather than two months or so on Ivory Gates?

I am probably too late, but just in case...

Yes, there are enough stacks of elves around your starting area to justify choosing the Elven Alliance over the artifact for the final mission, enough to level the field between you and the AI. Then again, I never played those games to get high score or finish the campaign as quickly as possible.

Wow, four years later, I'm really late for this one. Im a big heroes 2 fan and have played the game for a long time^^

I've struggled to beat Ivory Gates in under two months, but I think it can be done faster if you chose to rescue Jospeh instead of Ivan. This is because the barbs have weaker HP and spell casters seem to be more effective at hit and run tactics. If you rescued Ivan though, the other scenario is a cinch. You have to be ultra aggressive in the beginning but it gets easier as you go along. Just make sure you hire plenty of heroes to pipeline troops and keep exploring! (Having Ivan makes traveling through the mid-game swamp easier too!) I recently finished that scenario on the last day of month 2 (56 days) but might have been able to shave another couple days if I had planned some of my movements better.