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.