I would question that conclusion. There have been times in the past I've wanted to order from B&H, but could not because it was on the Sabbath. In most cases, I just keep looking until I found the item on a different website.
I'm sure they consider the loss of business worthwhile to comply with their religion, but there is a cost.
It may be less than you suspect because the regular bubble in their ordering pipeline might give them time to deal with suppliers, maintain stock, improve their website, maintain systems, relax and refocus, etc.
I doubt it works out better than not doing it at least economically, but there may be enough benefit to offset most of the costs.
The times I've run into the B&H sabbath outage, I just waited and ordered later. There are more thing in my life than just ordering things as fast as possible, and I respect a business for having other priorities. (Plus, B&H is just generally a really good supplier)
On a purely personal level, it's not so much the speed as it is the need to get it done and move on with my life. If I need to order something, I want to just do it and forget about it for a few days (or whatever) until it arrives in the mail. If I have to come back later, that's one more thing for my mental to-do list.
the thing is, the bubble they have includes not doing anything on this list :)
Save twenty bucks by placing the order tonight instead of right now? Sure, why not.
I also find it charming that they've managed to become a massive retailer while sticking to their religious values, although there are plenty of examples of that in other chains in the US that don't sit as well with me, personally (Chick-fil-A, Hobby Lobby, etc).