Hi Kristiana,
You must be so excited to be planning your Walt Disney World Resort vacation! I'm not certain what type of tickets you will be purchasing for your trip, so I'll do my best to cover all the bases.
Disney's current best value for tickets for military families is the
Disney 4-Day Military Promotional Ticket. These tickets are only good through early October 2015, so buying them in advance would not be a good choice for you at this point. It is unclear as to whether or not Disney will offer these again starting in October 2015 (generally the ticket offer is available from October through the following September), so stay tuned to the Disney Parks Blog and www.militarydisneytips.com for more details this summer.
Shades of Green offers two different ticket types that you can purchase: Stars and Stripes tickets and Magic Your Way tickets. You will receive a ticket voucher at Shades of Green (or your local MWR/ITT office if available to you locally) when purchasing these tickets. The reverse side of the voucher will give you the limitation and expiration information you require. You may consider calling Shades of Green (you can find their phone number on their website, www.shadesofgreen.org) directly and asking them about holding vouchers and using them at a later date.
I hope this information has been useful!
Best Wishes,
Amy B.