Forever, no. They can drag on if one side lets it happen or insists on using less than great planning though, this is not the fastest-paced of games (No, you are not going to have success in running up one of the small canyons to The Crown with your 2/3/4 mates. The enemy has the high ground, doesn't have to run uphill, and can respawn at the base. Better strategy is needed, involving quite a few more people and probably involving air support, vehicles, or sunderers.)
Its essentially a war, with changes made to suit a game and fun. Wars take time, effort, and logistics. (Thoguh it doesn't hurt to want to shoot the redshirts/blueshirts/purpleshirts for any number of reason, lore-based or nonlore-based)
Edit: Also, that involved a bridge. Bridges are special cases, since theres hardly much cover and if you can see one side of the bridge, you prooobably can see the other, which means you can shoot the bridgepeople.