Is it permissible to pray Qiyam al-Layl immediately after the Witr prayer, and what is the time interval between the two prayers?

The Sunnah for someone who intends to perform night prayers (Qiyam al-Layl) is to delay Witr until after them, based on the Prophet's (peace be upon him) saying: "Make the last of your prayers at night Witr." And for someone who has prayed Witr and then feels energetic enough to perform night prayers, there is no harm in him praying as much as he wishes without repeating Witr, based on the Prophet's (peace be upon him) saying: "There are not two Witrs in one night."