Most of my friends have kids. I sent mine out a month in advance to give everyone enough time to plan and find a sitter. I just had my shower yesterday and I sent out the invited at the end of March. Everyone had PLENTY of time to schedule the event. No excuses.
I heard 4-6 weeks. Originally mine were going to get sent out at around 2 weeks but my hostess decided to send them out 6 weeks prior. This way people can plan it, not only for the date but budget wise as well. Also, it gives you plenty of time to get R.S.V.Ps back. I think mine ask for them by 2 weeks prior.
I say 3-4 weeks before is good. Ours were sent out only 2 weeks before (not my fault) and there were quite a few people who couldn't attend because they already had other plans.
My goal when I send out invitations for a party is 2 weeks ahead at the latest. My best friend sent out the shower invites for my shower last week - it's May 31. She didn't ask me, but that seemed normal to me.
Re: How early should baby shower invitations be sent out?
we did a month in advance because some people may need to travel.
Mine were sent out today and my shower is 6/6.. so that is what.. 2 weeks
IMO, 6 weeks is preferable, 4 weeks is minimum.
I would set the RSVP date 1-2 weeks before, depending on scheduling constraints with caterers, etc.