Is it permissible to pray in a wide abaya from which a small part of the hand might be uncovered?

If what is visible from the hand is the back of the palm, then it is not considered 'awrah (private parts that must be covered), and the two palms are absolutely not 'awrah. Their uncovering does not affect the validity of the prayer. However, if what is meant is a part of the forearm, then it is 'awrah and must be covered.

According to the Maliki school, 'awrah in prayer is divided into a major ('awrah mughallazah) and a minor ('awrah mukhaffafah): Major ('awrah mughallazah): For a free woman, it is what is between the navel and the knees (her abdomen and what is aligned with it, what is between the navel and the knees, the buttocks, the thighs, the pubic area, and what is aligned with her abdomen from her back). Minor ('awrah mukhaffafah): The extremities (such as the forearms, neck, head, what is above the navel, from the knee to the end of the foot, and the chest and what is aligned with it from her back). It is disliked to uncover the minor 'awrah during prayer, and the prayer should be repeated within its prescribed time if it was uncovered.

Your past prayers are valid, and you do not need to repeat them once the time has elapsed, because repeating the prayer due to the uncovering of the minor 'awrah is only recommended within its prescribed time.