Invitations should be ordered when you have all the details of your wedding set: place, time of ceremony and reception, as well as your guest list.
Plan to place your invitation order at least 3-4 months in advance. Some companies may require 4-6 months, especially if you are ordering custom made invitations or handmade invitations and coordinating ensembles.
Depending on the intricacy of your design and because they are not mass produced, but rather assembled one by one, it can take anywhere from 4 to 10 weeks for your order to arrive. Also consider the factor of the design process, possibility of errors, proofs, and changes in your design.
Ideally invitations are sent 6-8 weeks prior to your wedding. It is best to send out-of-town guests their invitations 8 weeks in advance, as this will allow for making travel arrangements. Consider sending out-of-town guests save -the-date cards earlier, with information on hotels, flights and car rental.
Keep in mind that you will need time to address your invitations; ask family and friends for help. Doing it yourself is the most cost effective way. There are other alternatives you may want to consider: the invitation company may provide this service for an additional fee or send the envelopes to a calligrapher. A fun alternative would be to learn calligraphy yourself; there are many books and materials readily available.
Even though selecting your invitations may seem like a daunting task with all the possibilities available, giving yourself enough time will prove beneficial and a money saver.
It is never too early to start shopping around!