When I just had one, I arranged my work around her so that she was never left for more than 4 hours. Now we have three, and also live about an hour away from the nearest 'proper' shops/town, they do get left for longer, maybe up to 6 hours, but that is only very occasionally.

If we take one to a show and not the others, then we are out for a long day and I get someone to come in a few times and let the dogs out for a bit and have a play with them, but I would still never leave one alone for longer than 4 hours.