Generally speaking, for an event like a wedding, invitations should be sent out six to eight weeks before the event itself. If there are other factors such as events over the holidays or events requiring many of your guests to make flight arrangements to attend, you should try and send out your invitations ten to twelve weeks in advance. Alternately, you can send out a Save The Date card earlier and then follow the normal timeline for your invitations. Again, for less formal events, it is appropriate to send invitations approximately four to six weeks in advance.

Ultimately the choice is yours as long as you consider the farthest your guests will have to travel and the nature or formality of your event.  When in doubt, use a little common sense and always err on the side of caution.