I normally go up one or two levels per night, and usually play for a couple hours each night. So maybe 1-2 hours per level (obviously it will go up as the levels increase, but hopefully so will my score).
I know for some people like Nexus, who I've seen with 10,000+ score per game, whereas I normally manage about 5-7K per game (most I got was 11,000 I think, and that was probably because I was the gunner for Nexus in a tank )
Yeah i generally get around 4-10k in a map, all depends on the map, what your teams like and getting used to the map / patterns of play.
I only play for an hour or so, suppose i need to up my game so to speak !