I'm manually noting down durations in timedot format (https://hledger.org/hledger.html#timedot-format) in a text file.

For example, today's entry as of 18:32 is:

    2021-01-03
    leisure:anime       .......................
    leisure:social      ..
    sleep               6.5h
    chores:foodprep     .
    chores:regular      .
    leisure:social      ......
    leisure:ttrpg:play  ..........

Each dot is 15 minutes, so I'm missing a bit of time today. Oh well.

I think that having a timer app which lets me start / stop timers individually and give them names would be helpful. The one I'm currently using, on my phone, just has a single stopwatch.