In brief
For a good baked potato, start with a healthy tuber and clean it well. The size and specific oven affect the readiness.
Useful to know
When choosing potatoes look for hard, smooth tubers. The University of Iowa recommends avoiding sprouted potatoes, soft sections, and a greenish color. A cool, dark and airy place is suitable for storage. [1]
Before cooking, rinse under running water and scrub with a vegetable brush. When baking whole potatoes, choose roughly the same size so that you can monitor their readiness in a similar way. This is a practical organization of the tray, not a guarantee of equal time.
In the university example, potatoes are punched with a fork and baked at 425°F, approximately 218°C, for about an hour or until ready. [1] Use readiness as a crucial criterion: a large and a small potato does not necessarily have to be pulled out at the same time.
Do not confuse the conditions for raw tubers with those for a ready dish. After cooking, storage is a separate task; a warm kitchen is not a replacement for a refrigerator.
Sources
For further detail and to check the information: