It's nine hours of TV. He was probably working on it for less than a year in total (though not consecutively). I presume he's done loads of acting work since. Of course he doesn't remember it that well!
Not rewatched for a while but I always found it both funny and cringe (in a good way). But it also came out at pretty much exactly the time I was in sixth form, at a pretty similar sort of school. So possibly more relatable to me than to most!