You'll need a good storyline to keep people interested. How we've run 24hr games in the past is you have the two teams... and givew them some commanders, but you have field admins that are in radio contact with the team commanders at all times to keep the scenarios running smoothly and to do some improv if things get messed up a little. The key is to have it running smooth. Only way to do that is have VERY good communications between the teamleaders and the admins. On our field regular FRS radios don't cut it so we have a bunch of UHF radios we lend out to the admins and leaders for these types of games.
Also, some of the most fun 24hr games I've been to, we get on our teams and goto our main bases, but we get an hour or two to build up the defenses and make our "HQ" a very solid base. The games are usually planned to keep the majority of fighting away from the bases so that people who want to sleep at night, can. Those two main HQ bases should not be able to be captured by the other team. If things happen where they go through the base and clean everyone out, then thats cool cause it was probably a hell of a firefight, but they shouldn't be allowed to maintain control of that base for the whole game cause it gets pretty boring and frustrating for the team that has no base.
Be prepared for fighting to die down at night. So plan fewer scenarios for nighttime and make them a lot simpler. Unless everyone has nightvision or its a really bright night things are most definately going to slow down. I remember one 24hr game we had here in Edmonton... the enemy team had a base that was very well dug iin in a trench system and it was surrounded by fields so they had clear view of any attackers. It was night time and there want a lot going on so me and a few buddies headed out to raise some heck at the other teams base. halfway there we heard a few shots and some fighting going on like 209 feet from where we were so we hit the deck. We ended up staying there for the majority of the night in the prone, guns up and taking turns sleeping for a half hour at a time in the middle of the thick bush. About 4 in the morning the fighting stopped and we pushed forward to their base and got lit up as soon as we got near because a few guys on their team had gen3 NVG's. But it was fun. Night time fighting is very different simply because you can't see.