Do let them know
My dog comes to work with me but I used to leave her occasionally for a few hours or so, I thought she was fine, when we went xmas shopping she was left for 6 hrs and afterwards my neighbour came round to tell me she'd been barking for most of that time, he wasn't nasty about it, and I was glad he'd told me as I wouldn't have known otherwise and assumed she was ok being left (not for 10hrs a day; I mean for a few hours once or twice a week if I went shopping etc!)
He told me in a nice 'just to let you know' manner, I'm sure he was probably quite angry with me for having to listen to her yap for hours, but he was nice and polite and I have to admit my immediate concern was my dog that she'd been upset all that time, I apolgised to neighbour and there's no hard feelings (I hope!).
But now I know, and she doesn't get left alone at all, if I need to go somewhere she can't come, OH stays at home or she goes to a lovely dog sitter, costs me £5 for half a day and she loves it.
The joy of having a dog is the constant, never-failing companionship - you can't just ask the dog for that for the hours you're available, he/she's around 24/7.