Okay, now you've asked for a tiny app, and as any tiny app, this is missing features. But anyway. I've written one, very simple, that may do what you want.
You can Download it here, save this file somewhere, right click it, go to Properties → Permissions and make it Executable, then double click to run it. You can also create a launcher for it and add it to your Applications menu.
- Please note: I can't promise you to support this, like a paid developer would do for you, but I hope it's helpful none the less. But if you want me to do some little adjustments, just post a comment.
This will store all of the data in a file called
task_timer.json, in the same directory the file is run from (probably your home directory). You can change this directory at the top of the file. If the app crashes or doesn't start properly, run it from the Terminal (use
cd path/to/file and
./filename to run it) and provide the output, so that I know what's wrong)