Used to describe something that you anticipate will be belated (e.g. wishing someone happy birthday) had it not occurred at this instant (now), at a time which is earlier than "on time".
Most commonly seen on Facebook walls where one friend wishes another a happy "prelated birthday" (in case they forget to do so on the day of).
Wishing someone a happy Birthday before the date of their Birthday because you know you will forget on the day to wish them or will feel bad to wish them after.
Aye Breds, Happy Pre-lated Birthday!!! You KNOW I'm forgetful like dat!