Time frame for Bridal Shower invitations . . .

Wondering (I am in my friends BP), what is an appropriate time to a) send them out and b) put down as an rsvp?

I have been told to have the invites out anywhere from one month to two months before and to have guests RSVP anywhere from 1 week to 3 weeks before . . .

For the showers I've been invited to - its typically been about 6 weeks prior that I receive the invite, and 2-3 weeks prior that I need to RSVP.