My stepmother is planning a surprise party for my dad. She booked a restaurant and sent out invitations 2 weeks ago. The party is not until July 27th. She sent them out sooner than I would have sent wedding invitations. She just sent out a facebook message telling everyone the venue has changed, now she has to send new invitations. My aunt sent out her invitations too since they are having a joint party for my dad and uncle.
Realistically, what is an appropriate amount of time to send out invitations for a birthday party? I want to let my stepmother know so she doesn't send the new invites out too soon.