No idea, but to test them add the following to the init field of any unit or vehicle which weapons are handled by the player:
this addEventHandler ["Fired", {_tini = daytime;_round = nearestObject [_this select 0, _this select 4]; [_round, _tini, _this select 4] spawn{waitUntil{isNull (_this select 0)};hint format["%1: %2 secs", _this select 2, (daytime - (_this select 1))*3600]};}]
Fire any weapon pointing high and the even will give you an accurate value. Note that ammos with high drop rate might hit the ground before being erased by ArmA even firing them up vertically.