How far in advance do I send bridal shower invites??

I'm throwing my sister's shower. How many weeks before the date should I send the invite?

I was planning to have the shower April 21st but now her BMs are having conflicts... argh! That was the only weekend that was working for everyone and now they're telling me it's not good.

Her wedding is May 26th so I don't want to have her shower in May because I feel like it's cutting it too close.

It's too late to try for the end March at this point, right?

for a shower I'd try to get invites out about 4-6wks before final headcount is due. And remember just like a wedding you'll want a little buffer time to call the people who don't bother to RSVP.
good luck!