Hmm, i dont think thats ok imo, if you are out of the house that long 3 days a week it's cruel to leave a dog that long, even if you "get a walker" in the middle of the day.
They'll need the toilet, food etc. Especially young puppies, who are essentially similar to toddlers in that they need constant attention.
I also doubt any reputable rescue or breeder would agree to sell/give you a dog based on these hours. We were grilled by both rescues and the breeder.
I got a dog only after being self employed for a year and when I knew 100% that my business was going to work. She comes to work with me every day.
We leave her a few hours here and there but that was trained up over a period of many many months, maybe even up to a year where she was left for small increments of time until she got used to it. We'd never leave her longer than 4-5 hours but that would need to be an absolute emergency. Ie. We didn't know or couldn't anticipate being that long because something happened. In 5.5 years it's happened maybe twice. Shes a lazy girl and generally just sleeps thankfully. If we know we'll be longer, we leave her with a family member or i book a doggy daycare ifni want her to have some extra Socialising or just for a change. Hell, even if we go to the cinema, my mum looks after her for those few hours.
It might be wise to either think about getting a cat (super independent, we have 2 and 1 dog) or if you're adamant, see if you can adapt your work schedules or get more wfh days or do part time days instead.
My partner works in hospitality, a dog friendly place in the sense customers can bring dogs and when our dog needed 8 weeks of crate rest, his boss told him, as long as she didn't interrupt his work, he could bring her in to work!! He didnt ask, his boss just offered. As I have my own workroom I was ok looking after her since she came with me to work anyway so apart from making space for a crate, it made no difference. Ask your employers, They can only say no. (Assuming you are in a workplace that can potentially agree!) Some might be like "ooh puppy" and agree.
My only other suggestion would be doggy daycare for those 3 days rather than a walker. Socialising, well walked, fed, given lots of toilet breaks and stimulation. My one collects early morning and drops off early evening within certain time windows so it could just work perfectly.