The four dials, or clocks, are located on the HOS Screen in the driver app. These dials represent how many hours or minutes remain in a driver's Break, Drive, Shift, and Cycle clocks.
The top left Break clock shows the time remaining in a driver’s shift until their 30 minute break.
The top right Drive clock displays the drive time remaining in a driver’s shift until they are required to take a 10 hour break.
The bottom left Shift clock represents how many hours of "On Duty" time a driver has before they must take a 10 hour break. Commonly referred to as a "daily limit".
The bottom right Cycle clock indicates the time remaining on a driver’s cycle. This typically represents a 7/8 day or weekly limit.
You can view a brief summary of related HOS regulations directly from the FMCSA here.