How's your python. Its a pretty simple thing to make in python... It won't care about the platform you choose to run it on.
I'm at the pub right now, but for a quick solution... I made this. It'll save as a CSV as it goes.
Just tested on android ide so doesn't look pretty but I can make up a slicker interface if you want?? I can also package it as a binary and publish on github if you didn't find something suitable.
Enter the task name, hit start to trigger stopwatch, and stop when you're done.