Is the night prayer performed in 11 rak'ahs within 20 minutes considered a night prayer, or must it be longer?

The night prayer (Salat al-Layl) is not obligatory; it is a supererogatory (nafilah) prayer achieved by two light rak'ahs, as the Prophet, peace and blessings be upon him, said: "When one of you stands for prayer at night, let him begin his prayer with two light rak'ahs." Its validity does not depend on its rak'ahs being long, and the reward increases with the betterment and length of the prayer.