I've cooked in underground pits for some time, but usually on a larger scale. I just guesstimated on how long I thought this would take, considering the amount of hot coals I had in the pit too.
When cooking underground, you do not want any air seeping in, you could have flames. The idea is to have a deep enough bed of hot coals to last for the time you will need.
I think you and Monstah BOTH need to meet me in Florida for rum on the beach! Wouldn't that be fun! LOL! Maybe we could find a wedding to crash.