I would say do what has given you good results before. If 48 hours has worked for you, then stick to it. The last batch I kegged, I set it to 30 psi for 24 hours, then dialed it down to 12 psi. It took a few more days for the carbonation to be to my liking. I left it at 12 psi throughout the entire keg and felt it was slightly overcarbed by the end. Next time, I will do 30 psi for 48 hours, then dial down to 10 psi. My beer lines are 5 feet long and I usually set it and forget it at 10 psi for 3 weeks. This method usually gives me perfect carbonation but Im not patient enough to wait that long all the time. I also cold crash.