It seems that it was stated in the listing information, which guests should read thoroughly before booking. I think the host's hours of heating are quite strange, but you did agree to what the host states in their listing, regardless of whether you missed reading it.
I would imagine that the price you paid for the accommodation was discounted because you have a long-term stay, and it's reasonable that the host couldn't absorb any further costs for what he charges. So you just have to honor what was written in the listing description- if that means you have to pay more for the extra electric you consume, so it goes.
I'd speak to host and find out how much his bills are per KWH so you have an idea of how much the daytime heating would cost.
I do sympathize- I hate being cold and wouldn't book a place where the host was stingy with the heat. Which judging from my reading of posts on this forum over time seems to be quite common in the UK- that people just walk around in bulky sweaters in the winter to save on heat.
@Andrew2147