I'm guessing you might be from Great Britain? I'd heard of B&Bs there with part time access (even "part-er" than you describe, because one is not even allowed to stay in one's room during the day) but I thought that must have died out by now.
I've came across some Airbnb listings in the London area, that have some very strict curfew rules.
The hosts basically: "We primarily rent out to tourists. As tourist we expect you to be outside the house from 9am to 5pm."
Well, I've shown these listings to some of my friends and there were disgusted.
Even if you travel on business, there might be ocassions that you cannot access the customer side and have to do your conference calls from your hotel room.
But generally speaking, the curfew restrictions are being waved by more and more hostels. It was standard practice 20 years (for security/cleaning) to bar guests staying there between 9am and 5pm.
Hostel mgmt. probably have understood that the today's travellers do not want to be told when to get up in the morning.