If a user is logged into their DeskTime app through the desktop application and the internet connection is suddenly lost, DeskTime will go offline (Linux and Windows users DeskTime icon will appear red, MAC users will say it is offline). However, the data will be collected locally on the computer until the internet connection is re-established. Afterward, tracked data will be sent back to your application.
Please note that stored data will be lost if the user's computer is restarted during an offline period. In that case, the lost time can still be logged manually. Find out how to do that here.