Well, a minidisc encoded in LP4 plays for like 5 and a half hours. that’d be 11 half-hour tracks. 
In other news, I improvise an hour of ambient once every couple of months for a lunchtime meditation session at the university where I work. There’s one coming up if anyone fancies a trip to Swansea - I’ve also considered streaming it in the past, but I’ll record whatever I come up with.