You should do both as soon as is reasonably within your ability. Neither is heavily enforced, but you don't want to be the guy who moved here a year ago, now has expired license and registration, and is hitting snags getting them changed over. Getting a license should be simple, as long as your prior state license is valid. Believe you can provide two proofs of residency and the old license at a driver center. The registration may be tougher, if you don't have an actual title for your vehicle (lien?). Any notary service that is an issuing agent for penndot can help with this, such as a AAA branch. If you have the title, it's much easier and a bit cheaper. Again, few officers are going to cite you if your prior state credentials are still valid and you explain you recently moved, whether it's 21 or 61 days ago.