Landru, I was sure my husband would know who Landru the character on Star Trek was. Alas, no.
Anyway, a 12 week old puppy can, in general, only be able to to hold their urine for the number of months of age they are plus one. So at 12 weeks, or about 3 months, (3+1) 4 hours is about the max during the day. I did keep my older boy in a crate while I was at work when we first got him. Someone would come home at about 4-5 hours to let him out. He did have an accident or 2, but they grow fast and soon he was OK, no accidents. My younger girl also stayed in a crate while I was at work and at 4 months of age she was still dry after 8 hours in the crate. I did attach a small water bowl to the side of their crate. Some of the others on here did put their pups in a play pen or exercise pen rather than keep them crated and it has worked out OK. Hopefully Snowshoe or sparky or some of those who have used a pen can give you their thoughts.
My only comparable experience was our very first 2 dogs before I knew anything about crates. We left them in a small, contained room with newspaper for them to urinate on if needed. Every. single. day. we came home to pee'd on papers that were torn up and thrown around all over the place. They never pee'd in the house on weekends when we were at home, they didn't need to go out in the middle of the night pretty quickly, but every. single. work. day. I don't know how old they were before they no longer pee'd in the house. Six months? Older? probably. By the time we figured out that there was such a thing as a crate they were really old enough to go 8 hours without peeing.
Fortunately, he's getting older and bigger every day. It won't last forever no matter what.