Small potatoes typically take about 20 to 40 minutes to cook in the oven, depending on their size and the oven temperature. Here are some common guidelines:

• At 400°F (200°C), small potatoes cut in half roast for about 20 to 30 minutes until tender and golden brown.

• At 425°F (220°C), halved or quartered small potatoes take about 25 to 30 minutes to become crispy outside and soft inside.

• For whole baby potatoes, it can take around 30 to 40 minutes at 400°F, arranging them cut side down on oiled baking sheet for crispiness.

In summary, roasting small potatoes in a preheated oven at 400-425°F for 20 to 40 minutes works well. The potatoes are done when they are fork-tender and golden brown on the outside. Flip or shake the pan once or twice during cooking for even roasting.