Джон приступил к работе в 3 часа, а

Джон приступил к работе в 3 часа, а в половине четвертого он ее уже закончил.

Результаты (английский) 1:

John started to work at 3:0, and half of the fourth, he's already finished.

Результаты (английский) 2:

John started working at 3 o'clock, and at half past three, he had already finished her.

Результаты (английский) 3:

John started to work for 3 hours, and the half of the fourth he had already finished.