What is qiyam al-layl? Qiyam al-layl means spending the night, or part of it, even if it is only one hour, in prayer, reading Quran, remembering Allah (dhikr) and other acts of worship. It is not stipulated that it should take up most of the night.
It says in Maraqi al-Falah: "What is meant by qiyam is spending most of the night in worship, or it was said: spending one hour of it, in reading Quran, listening to hadeeth, glorifying Allah (tasbeeh) or sending blessings upon the Prophet (blessings and peace of Allah be upon him)." (Al-Mawsoo'ah al-Fiqhiyyah al-Kuwaitiyyah, 34/117)