International Driving Permit

(You've accidentally posted your message twice, so may wish to delete the duplicate. I posted a quick note on that thread to try to direct responses to this thread.)

The IDP (assuming you are talking about a US issued one) is valid for 12 months, so you would want to wait at least long enough for it to be valid throughout your trip. If you're taking multiple trips, you may be able to time it to be valid for both.

Beyond that, it typically only ever takes me about 15 minutes at AAA to get mine, and I previously never needed an appointment, though that may have changed.

AAA will generally ask which date you want it to be valid from, so you can get it early. We normally pick the day our trip begins.

Getting your IDP from AAA is quick and easy and in my experience you can save a few bucks if you take in your own photos (I get mine at CVS). I usually go 3-4 days before my trip.

As I recall, they're only valid for one year or until your state drivers license expires, whichever comes first (subtle point). My AAA (each state's AAA is an independent business, with different rules and policies) would only date it from the date of issuance, so worth asking ahead of time. Its done on-site so you don't have to wait for a mailing or processing. But worth calling AAA ahead of time IME as not every person there is authorized to do them.

AAA will generally ask which date you want it to be valid from, so you can get it early. We normally pick the day our trip begins.

That's been my experience.