How long does it take for invites to arrive in Europe?

We have 10 invites that need to be sent to Italy. I was going to send them tomorrow. The rest won't be ready to go out until next week (various issues with inserts, etc).

How long do you think it will take for the invites to make it to Italy.

Also, I didn't put stamps on the reply cards for the Italian invites. Do you think there's any way that a US post office could provide that?