If you have the date time and venue picked, there is no reason why you cant send out invites now.
But if you havent then I would definately send out date cards now. there is nothing worse that people not being able to come to your wedding due to earlier commitments.
Gives people enough time to plan and pay for flights etc if needed or organise babysitters and what they are going wear! lol

Good luck with the rest of your wedding planning!