TEX, you have some splain' to due!!!
FYB, bomb delay is 1,000ft of travel. If you drop a bomb standing still, the bomb must be 1,000ft above the ground so be armed.
If you are flying at 500mph, you can be below 1,000ft. The bomb will fall at a diagonal and therefore still travel the 1,000ft in the air while your plane is less than 1,000ft above the ground.