Is there a huge amount of home brewers in your area? I can't see this as being profitable. There is rarely a time when I'm missing something and if I am I'm not going to pay marked up prices to get it that day, ill just postpone my brew day.
I'm not trying to rain on your parade, I just think the 24 hour part won't work. Plus your not going to want to get up at 2am because I'm drunk and forgot 4oz of malt and about to mash in
Also they might have "rubbish" hours because maybe thats all your market will bear. If he was open all the time it might not be as profitable for him.