Shipping and registering a car

So I'm not sure if I'm understanding this right. Once you pick up your car from the port in San Juan, you have three days to register it? But in order to register it, you need to show a local residence?

What if you just got there and you're still looking for an apartment?

How do people handle this (or have I misunderstood the problem)?

I don't think they can hold you to the three days when you can't even get an appointment to register it that fast. My advice is don't do anything to get pulled over, and in addition to a lease, utility bill or bank statement with the address don't forget your passport, social security card (original, not laminated) and birth certificate...I kid you not! I picked mine up Tuesday, stopped off at cesco in Arecibo Wed. They told me since I was renting in Rincon I had to make an appointment in Aguadilla (even though I am closer to Mayaguez) to register and the first available is Monday.