What should someone do who has a wet dream and is delayed for Fajr prayer or school because they are waiting for water to heat up for ghusl, and must they make up the prayers they performed while junub out of ignorance?

Warming water for ghusl (definition) is legally required if a Muslim is harmed by using cold water. If a Muslim sleeps after the prayer time has begun, knowing or thinking that they will not wake up before the time expires, they must repent. However, if they wake up after the time has expired, or before it expires but with insufficient time for purification and prayer, they must perform ghusl first. Being late for school is not an excuse for abandoning ghusl; rather, ghusl and prayer must be performed before going. Prayers performed without ghusl must be made up, unless the Muslim adopts the view of Sheikh al-Islam Ibn Taymiyyah, who held that one who is ignorant of a condition or pillar is not obligated to make up the prayer.