My little writings on announcement cards
You are showing consideration for your invitees by allowing them enough time to set aside the date and shop for an appropriate gift. A longer lead time also gives you leeway to invite alternates if any of the original invitees decline. The invitations should go out no later than two to three weeks prior to the date. Four to six weeks before the shower date would be better, particularly considering how busy the schedules of most people, especially parents, are these days. Many of your guests most likely are busy young parents themselves with sporting events, play dates and family obligations to contend with.