How often should I take my dog outside to see if there is blood in his stool?

Doesn't your dog let you know when it needs to go potty?  You can take your dog out often but that doesn't mean he is going to poop unless he needs to.  Just wait it out & he will go when he needs to.  You can't force a dog to poop, you have to wait, even if it takes several hours.

Every hour of your life. Since you want to turn your life around for a dog. 

Quite honestly I find it odd that a vet would tell you that.   I'd take the situation into your own hands (not literally) and collect some of his stool soo your vet can do a fecal test to diagnose what IS going on there.    He may have Giardia or some other internal parasite and the sooner this is identified, and treated, the better.   You shouldn't sit and wait.    Poor boy, small wonder he's confused.com.

ps   Blood in a STOOL won't be a Urinary Tract Infection!!!   UTI = Infection in the Urinary Tract.

I find it ODD - if you (really) have a dog and feed the dog at regular intervals, that the dog does not have "regular" POTTY times for passing his stool.  Most puppies begin (during housebreaking) by going to pass a BM shortly AFTER eating.

Okay (for the sake of argument) if the dog is now IRREGULAR, then wait until he asks to go out, and GO WITH HIM.... so you can OBSERVE whether he has:

1) a stool and 2) whether there is any blood.

Is that SIMPLE ENOUGH?

........and when your vet said 'to monitor him' did your vet also tell you the date/time for the appointment? NO...no vet would tell you  'to monitor' if you had bothered to phone, they would tell you to go and take your dog to the vets asap ... so instead of your self adviced monitoring........ PHONE your vet and get it in asap to see the vet as blood in the stool could be a blockage could be a UTI or could be many things ALL NEED INVESTIGATING AND TREATMENT