It appears to be that the radio clock display has malfunctioned, and is due for a replacement radio, which could be an aftermarket or oem radio, maybe found at a junk yard.
Tools required for oem replacement radio, torx keys set.
Before working on the radio or other electronics, disconnect the battery cables with 8mm wrench.
Replacing the oem radio is much easier, if you obtain oem radio, compared to aftermarket radio, due to being direct fit.
The radio is same for 1995 to 1999 Pontiac Sunfire and the Chevy Cavalier, regardless of sub models, such as SE,GT, VL,VLX,Z24. etc.
Parts needed for the the aftermarket radio install :Stereo assembly, stereo wiring harness adapter, radio antenna adapter, and dash install kit.wiring diagram for the wire colors / functions, along with tools, such as torx key set, screwdrivers,wire crimper, wire stripper, double ended wiring connectors, hair dryer.
The oem stereo removal video is for the 2000 to 2005 Sunfire / Cavalier, but are the same or very similar procedures.
Link to oem stereo removal procedures.
Pontiac Sunfire Radio Repair and Removal 2000 2005
Link to aftermarket stereo install / connect procedures. ( Sunfire Video )
HOW TO INSTALL AFTERMARKET STEREO PONTIAC SUNFIRE
Link to aftermarket stereo install / connect procedures. ( General Video )
How To Install Car Stereo Single Double DIN Car Audio 101
Have a nice day.