It is important to our development organization to keep time tracking records of what we work on. We have to bill customers and keep track of other time for management purposes. It would be very helpful to have such functionality within Phabricator.
I'm sure there are many other development organizations that have need of tracking their time as well.
Kiami is a PHP based open source time tracker that is clean and easy to use. It might be nice to work with them to make Kimai so that it can also be installed as a module for Phabricator. This might bring this functionality to Phabricator faster than writing something from scratch.