Turn it to serving pressure. If you're going to keep it at 34F, that's about 14 psi on the high side. Leave the gas connected and don't rock it, shake it vigorously for about 10 minutes total, take as many breaks as you need. It will be pretty well carbed after that, but you can check it and do it some more as needed.
If you leave it at 28psi you'll probably end up with over carbonated beer. If you leave it at serving pressure you can eliminate that worry.