Leaving him for 12 hours straight is not good, he can survive but not it's recommended to do. If it was for some months then you could hire a sitter.
The first few months are crucial for you to be with him for puppy's development, but if you send it to training home then it will also work although you being there in person with him through out the training, is way better.
Getting a puppy is a commitment for 10-13 years, given you can sneak out at lunch but can you keep that up for those years?
I work 8 hours a day for 6 days a week, my wife does the same but my sister is home to take care of him while we are away.
4 hours, i think is max for a puppy to be alone.
But i guess, he will survive with your schedule, if not thrive.
But this is my noob opinion, please let the senior and experienced member be the judge.
Robean Gyalchen Lamakhor.
Tyson GSD 09 JUNE 2013
Rusty BOXER 12 Jan 2009 to 25 Oct 2012