By the time I finished all the bombs in the main game, I had defused 31 total.
The easiest way I found to defuse the last 69 was to start up the mission 1.3, "The First Bomb" and quickly defuse that. It took anywhere from 7 to 40 seconds each time, for about an hour and a half for grinding.
Every bomb will be randomized to an extent. They will all have a wire module, a button module, and a keypad module, but the solution is generally different each time. Just have the manual pulled up (even though that's cheating
), and use the solutions on there to solve the bomb. After you defuse a few, you'll catch onto patterns and will be able to solve them even faster.