Oven takes a long time to heat up

Oven/Range/Cooktop Repair
1

Brand: Samsung
Model Number: NX58J5600SG
Main Symptom: Oven preheats slow
What happens & when: The oven takes a long time to reach desired temperature. The oven’s flame rapidly turns on and off. It does eventually reach the desired temperature.

Error Code (if any): none
Parts or tests already tried: Removed the 2 covers off the burner and monitored the flame.
Photos / video link:

2

The place to start will be with a multimeter checking the ignitor, safety valve, and oven sensor/probe.
https://www.appliancepartspros.com/repair-help/