Giveaway must start after the current time.

Set the time to 10 minutes in the future?

change your gmt+ time

sacrifice a virgin.

but the suggestion of Lorkhan could work, too

Build a time travel machine, get back to the far past, and kill Adam.

but the suggestion of TheDopeFish could work, too

It means you took too long writing the description/other details of the give away that the initial time you set for it to start is too far into the past for the system to accept it any more. Just move the start time up to about a minute or so after the current time if you want it to start immediately.