On Vahmana incarnation of Lord Vishnu, He went to King Bali to get all lokas from him. After taking all lokas and Bali himsef from him He got pleased by Bali's comitment (vachan palana) and grant him boon that in savarni mantav (time whose exact name don't remember right now) you will get post of my great devotee Indra. Till then you go and live in sutaka loka with your grand father (Prahlad).
I am not sure whether Lord Vishnu grant post of King of heaven or some other post. And what is the time when he will get that post of him. What was the exact boon that Lord Vishnu gave to King Bali?