Many oven cleaners work overnight. You might have to use some elbow grease, but it's still easier than 50 years ago. Be sure the oven is completely rinsed clean of oven cleaner residue. You would not want any of the cleaner to be in the oven when you cook. Depending on how often there are spills in the oven, you should plan on cleaning your oven on a monthly basis.
Microwave ovens are simple to clean.
All you need is water and dishwashing detergent. Wipe clean and dry. be sure to clean the oven door, too. Clean the window with window cleaner. Cleaning your oven may not be your favorite chore, but it is a necessary one. Excessive spills can cause smoke and offensive fumes.