If you would like to track time automatically on projects, please turn on time tracking and select the option to auto time track in company preferences.  - See how to turn on time tracking

Once auto time tracking is turned on,  the system will track time on projects automatically as you open and close projects.  When you open a project, a window with a timer will show up in the bottom left corner of the browser.  The timer will start counting in red and then turn green once the time goes above the minimum threshold you set in company preferences. Here is what the timer will look like before and after the threshold you set:

When you leave the project, the time you spent on it is saved as is, but by the end of the day, the time is rounded up to the "round recorded time" you selected in company preference.

You can always go to the project "Time Tracking" tab to edit an entry if you need to.