Well the next best thing is, as postwick stated, Unidad. If you engage them you can have a blast for as long as you desire and bail out at any time. A buddy and I got bored one day because we both have our maps 100% clear of missions, so we engaged the Unidad and just kept killing them for an hour and a half without moving from our position.
There may not be a timer, but you will not ever run out of enemies with that. Just find a spot where you can fortify near Unidad and open up on the little bastards. Lots of people on these forums complain about the Unidad, but honestly they are one of the most fun elements in the game
Nothing like holding off the entire Bolivian military for however long you want (which is admittedly easier in real life than in this game hehe).
1 people found this helpful