They used the "army" 24 hour clock.
Bells were there for men who couldn't afford a personal timepiece.
Midnight= 8 bells 12:30 = 1 bell, 01:00 = 2 bells, 01:30 = 3 bells etc.... the end of the watch at 04:00 was 8 bells which is why we hear "Eight bells and all's well"
If they wanted more accurate time, they would have needed a personal timepiece.
I mean, how would they have said 04:02 ? Eight bells and two tinkles? That would have just been wrong to say on board.