I take mine from room temperature and put it in the Keezer. As it is chilling I put about 35 to 40 PSI on it. I check in 24 hours. Normally, It's chilled and almost the right carb at that time. Sometimes, it will come out just slightly under carb'd and needs another 4 hours or so at 35 to 40 PSI to get to the right level of carb. Then turn it down to 8 PSI for serving. One thing, make sure to burb the pressure relief air lock after bringing the pressure down otherwise it is still at 35 to 40 PSI in the Keg eventhough your regulator may say only 8 PSI.
For Nitro, I take mine from room temperature and put it under CO2 for 24 hours while chilling at about 20 PSI. This half carbonates it and makes it ready for the Nitro. I then put it under 35-40 PSI of the Nitro beer gas and rock/shake for 15 minutes. Let it sit for a half hour and serve under nitro pressure of about 35 PSI. Watch the pretty cascade.