Thanks for your response! I'm using "TimeTrack" for Android to track my time. With the app, I added a widget to my smartphone home screen and I fiddled with the setting to achieve the following:
* Good to know, I can unlock my phone with my finger print, so if I "grab" it in the right way, it automatically unlocks as my finger exactly hits the finger print scanner.
* If I "start" a new category of time, the previous is automatically stopped;
* I have the following "shortcuts" right on my home screen;
An average time-switch-registration takes me < 10 seconds, including taking my phone out of my pocket, tracking time, and putting it back in my pocket.
"TimeTrack" has a good export-to-csv option, which I do periodically (once a day to once a week). I then overwrite a Google Drive sheet that I have with this said export. My website automatically "reads" that Google Drive file so making the graph is no effort.
This manual export, including the import to Google Drive sheets, takes about one minute.
Total time spent tracking my time: 3 minutes and 43 seconds on average, every day!
~150 "time category switches" per week, so that is 1500 seconds + 60 seconds for the export.