Does my work start at 9 am?
My work doesn't start at 9 a.m.
Я думаю что будет так
My work begins at 9 o' clock.
Does my work start at 9 o'clock?
My work doesn't start at 9 o'clock.
обратите внимание на Ваш изначальный пример. в нем пропущен суффикс -s в глаголе
Does my work start at 9 am?
My work doesn't start at 9 a.m.
Я думаю что будет так
My work begins at 9 o' clock.
Does my work start at 9 o'clock?
My work doesn't start at 9 o'clock.
обратите внимание на Ваш изначальный пример. в нем пропущен суффикс -s в глаголе