How can one combine the Sunnah of eleven rak'ahs and prolonging each rak'ah during Qiyam al-Layl within one hour? And is it sufficient to pray two long rak'ahs to achieve the purpose?

It is not possible to combine the Prophet's long standing (in prayer) with praying eleven rak'ahs in a single hour, for his rak'ahs were very long. It has also been authentically reported that the Prophet, peace and blessings be upon him, used to pray Qiyam al-Layl with seven and nine rak'ahs as well. It is sunnah to pray Witr with one rak'ah after two long rak'ahs. There are disagreements among scholars regarding what is better: prolonging the standing or increasing the number of prostrations, but the most important thing is not to abandon night prayer.