I'm having a tough time envisoning a timing device for a cannonball though
Well the mortar tech then went into cannon shot, and then into cannon conical projectiles, which is why they are now not called "shot" but "shells" as their older ancestors, mortar shells, and even older ancestors, fireworks shells.
The original mortars were very similar to their much improved CW munitions..., in the 17th and 18th centuryies..., a wooden plug holding a fuze was inserted into a hollow iron "shell" that had been filled with black powder. The idea was that the fuze would be protected in flight, and would be apart from the black powder within the shell, until the fuse burned far enough and the fire reached the black powder within, and burst the shell..., but this was inconsistent, so over time, additional projectiles as you see in the above photo of a CW era shell, were added...
So at first, the mortarman lit the fuse on the shell, and then fired the mortar. The fuse had been tested a short while before the plug was inserted into the bomb with an unlit portion of the same fuse. Thus in theory, if the gunner knew the bomb would land on the target in 10 seconds, and 2" of fuze was burned per second..., then a fuse a bit shorter than 5" would set off the bomb just as it arrived overhead of the target. OR a little longer fuse in a very heavy shell would allow the shell to impact through the deck of the ship, and detonate within the gundeck, below.
Serious problems for the gunner, IF the fuze was "too quick", or if the mortar failed to fire!
THEN they found that the fuze would actually be ignited by the fire from the mortar, as the shell was launched, and the gunners stopped manually lighting the fuse before firing.
The principal and use then transferred over time to cannon shells.
'The bombs bursting in air" in our National Anthem refers to ship fired mortar shells...
LD