This app can track your work time easily! You can automate time tracking using geo-fencing functions (see below). You may also categorize each recorded interval by a predefined client/task and a free text. Of course, the list of clients/tasks can be edited to suit your needs, and the app has a widget for your home screen.

Additionally, if you wish, your flexible time account is taken care of: you always see how much you worked. You can also keep an eye on how much work time is left for today or for the current week (by a notification
which you can enable).