Not clear on Roma Pass procedures.
I will be in Rome for 2 days, leave for 5 days, and return to Rome for 7 more days.
Must I validate the pass immediately, or can I buy it and validate it when I am ready to use it?
No - you can "validate" it when you return... I have a couple of "packets" sitting at my house that friends buy from me... as long as you do not use the either card, you're okay to use upon return. We've never had a problem and have done it 6/7 times for folks coming from the States!
Ciao,
Ron