Did you say time travel?
What is it that makes time travel possible?
Non, non, non, non.
Not time TRAVEL.
I said "What makes time tracking possible?"
And delightful time tracking at that...
Toggl - it's completely free.
You can get a timeline view by project, to ensure you are focusing on your ONE THING.
If you're not familiar with the ONE THING framework (and even if you are), you really should check this out:
(Question to define: What's the ONE thing you can do such that by doing it everything else will become easier or unnecessary?)
...which will ensure you focus on what's important to get extraordinary results.