The problem I see as a game plot is: how do you drive home the temporal aspect to your players without them being the ones who are time traveling? Especially if all that is coming back is information.

Terminator worked as well as it did because you had the actual Terminator back there. A nigh-unstoppable force that was obviously from the future. The movie wouldn’t have been anywhere nearly effective if the war in the future had been between two groups of human with one trying to stop the other.

If chronomancy is the center point of your game, then it needs to have a huge emotional impact if/when your players learn that. If they aren’t in a position to influence the time travel aspects of things, then do they really matter? In fact, if you aren’t extremely careful it can present itself as railroading.

Using your example above (and assuming the players side with the elves): orcs are fighting a battler against elves. They have the new advantage of knowing how the elves won last time (plans) and the number of elven troops (forces).

How do you make it matter to your players that they got that info from time travel as opposed to really effective spies, or traitors, or some other contemporary means? Unless there are concrete actions they can do to affect it, it doesn’t really matter. And you run the risk of the players saying “Well, it doesn’t matter what we do because they’ll just get all our info through time travel anyway”.

Because that was the one big problem with the Terminator series. Since it worked on altering history instead of alternate timelines, Skynet shouldn’t have sent two Terminators back. They should have sent a lot more. Because as long as your future hasn’t changed, you know it didn’t work.

Run program: Send one back.
If still losing Then Run Program Send One Back.

I assume you can conveniently explain it as they only had time to send two, but hey.

You’ll need something in the present that they can do to deal with it. A “Miles Dyson” or some other figure/object/entity that they can somehow learn about that they can use to accomplish their end game (whether it is stopping the future war altogether, making sure one side wins, or just making sure they survive to see it). For example, chronomancy is developed by an Orc wizard 50 years in the future. If the orcs are winning the future war, do they try and stop this development by killing this Orc’s parents?

I’m not saying this can’t be done, but it will take a lot of careful planning to make an emotional impact, and careful GMing to make sure you don’t railroad the plot.