When a mud cake is cooked fully the top of the mud cake crust should be fully set and the edges may be brown and may be pulling away from the sides of the cake pan.
Also if your mud cake is fully done it should have a springy feeling to it when you press down on the mud cake the cake should easily spring back.
Also if you use a meat thermometer in the mud cake and it reads 195 F or above and no cake batter comes out on the cake thermometer or on a fork then the mud cake should be fully done.
The time it takes to bake a 9 inch round cake is between 30 to 35 minutes at 350 F degrees.
Preheat the oven to 350 F degrees and then place the cake into the oven on the middle rack and then set a timer for 35 minutes.
Check the round cake after 30 minutes to see if it has fully baked and if not allow the cake to cook or bake another 5 minutes.
If you put the cake on the very bottom rack that is too close to the heating element or heat then the cake could crack because it's getting dried out and getting too much heat.
So make sure to put the cake on the middle rack when baking the cake.