Pioneer KEH-P2800R Operation Manual page 45

Time Display/Setting
Displaying the time
Hold for 2 seconds
The time display disappears temporarily when you perform another operation, but the time
indication returns to the display after 25 seconds.
Setting the Hours
Hold for 2 seconds
Setting the Minutes
Hold for 2 seconds
When you release the DISP/Clock button, the second count begins from 00 seconds.