At the time of the final devastation of the complete universe [the end of the duration of Brahmā’s life], a flame of fire emanates from the mouth of Ananta [from the bottom of the universe]. The yogī sees all the planets of the universe burning to ashes, and thus he leaves for Satyaloka by airplanes used by the great purified souls. The duration of life in Satyaloka is calculated to be 15,480,000,000,000 years.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
अथो अनन्तस्य मुखानलेन दन्दह्यमानं स निरीक्ष्य विश्वम् । निर्याति सिद्धेश्वरजुष्टधिष्ण्यं यद्द्वैपरार्ध्यं तदु पारमेष्ठ्यम्
atho anantasya mukhānalena dandahyamānaṃ sa nirīkṣya viśvam | niryāti siddheśvarajuṣṭadhiṣṇyaṃ yaddvaiparārdhyaṃ tadu pārameṣṭhyam
SB 2.2.26