Adding a Clever Timer to a Spreadsheet

Hi there, I'm hoping somebody might be able to help me please!

I am watching live sporting routines (artistic swimming), where I create a string of characters, pushing 1, 2 or 3, depending on the error that I see.

What I would like is the following for each routine:
- When I press the 's' key, the timing begins.
- When I press the 'f' key, the timing ends and clears,
- Any time I press a '3' key, the stopwatch records the time it was pressed during the routine (see the last 5 cells in the screen shot)

Basically, I have the spreadsheet set up with no timing function at the moment, but would like it to record when in the routine I see a type 3 Major error.

This is way too difficult for me, but I'd really appreciate it if someone can work their magic for me!!

Many thanks in advance...