Mine are left a max of 4-5 hours very occasionally (every 3 months or so), and about 2-3 hrs once a week. Otherwise they are with me. When I leave them I make sure they have had an good walk and been fed so they settle and sleep off the exercise and food. Under 10 months, I crated the youngster until I was sure she would get up to no mischief!
Mary

china can be left from 8.15 to 5.30 and is more than happy! she sleeps all day!!

but then she sleeps all day everyday!

I'm home every lunchtime, so four hours is usually the maximum. I have, however, left them for seven before now, and they were fine (it was unavoidable) but if I know I'm going to be out longer than four hours, I arrange for someone to come in and see if they're ok.

When I was working, my previous dog was left max 5 hrs, but mostly went to work with my hubby.
Now we are retired so Mo has us all day every day. Of course there are days when we have to go out and days when we will be out for a long time. On these occasions we have a very obliging neighbour (owner of a Westie) who pops in to let Mo out for a wee or to just keep her company for 10 mins

I've left them for 8 hours once but they generally dont really get left alone for long periods of time. However, i'd leave them for a 6 hour shift, but i'd make sure their daily exercise didnt suffer.