Diagnosis
The clock/control board is losing its memory. There's no backup battery, so this points to a power interruption or a failing board.
How to Fix It
First, check for a loose electrical connection.
1. Turn off the circuit breaker for the range for 2 minutes.
2. Turn it back on and immediately set the clock. Use the range normally.
3. If it resets again, the control board is likely faulty and needs replacement.
If That Didn't Work
The problem could be a failing thermal fuse on the board or a wiring issue in the terminal block where the power cord connects. A loose neutral wire here can cause intermittent power loss to the controls.
Heads Up
This is almost always a board issue, not the clock display itself. Replacing the main control board is the definitive fix. Document your clock settings before the power cycle, as you'll need to re-enter them.