Hi,
When the oven ignitor becomes weak it won't make the gas safety valve keep a constant flow of gas, thus it will keep cutting OFF and ON like that.
You'll need to check the amps first from either of the two oven igniter wires.
Amperage range is 3.3 - 3.6 amps. You will need a Clamp style amp meter to check the amps when its ON and GLOWING.
If the Amps are lower than 3.3 amps when its ON and GLOWING, then your oven igniter is weak and will need to be replaced.
Here's the oven igniter for your model:
DG94-00520A Assy-Hot Surface Igniter
Another member had this same problem and I said the same thing to him and you can see it fixed his:
Appreciate any help with this issue. When turning on oven bake, ignitor glows, after 20 seconds gas comes on, ignites, burns fine, but then gas shuts of after 15-20 seconds. Ignitor stays glowing, after 15-20 seconds gas comes back on. It keeps repeating this, with the time between turn on /shut...
www.applianceblog.com
Let us know what you find.
Jake