# Set this setting to 1 if you want your bot to expire bans/exempts/invites set
# by other opped bots on the channel.
set force-expire 0
inside eggdrop.conf (or used to be in 1.6.21 last time I checked). I never used this and sounds like would do what you are looking for. Since the duration is set into the configuration this means you would need to make a piece of code to alter the time. Keep in mind this is a global setting, meaning it would lift bans from all channels it has channel operator status on.
Safest option would be a separate script with a channel based setting. I could help you with this but will take a bit cos I'm a bit busy with stuff at work.
Once the game is over, the king and the pawn go back in the same box.