When gracie was a 3-5 months I would always make sure she was only in her crate 2 hours or so I just didnt feel right leaving her in there. I knew that when I was home she was going out to potty about every 2 hours sometimes sooner than that she I knew that until she got bigger that 2 hours was the max in her crate. Now she is 7 months and she does well will pottying so she is gated in my spare room when I am gone and she does well for about 4-5 hours. I guess every dog varies. I think if you gradually work with your puppy or dog they will adjust to just about any schedule. I dont of course recommend an 8 hour day in a crate right off hand....or never really but if its necassary I say its your dog
I wouldnt feel good about that.