There is no specific time, date or day mentioned once a prappana sheds the mortal body, as it is stated that a Prappana travels via the Archiraadi Marga (illuminated path) to reach the Vaikuntam without any delay.
Sri Bahsyam mentions about reaching Sri Vaikuntam. The pasurams ‘Suzhvisum pani mugil’ and ‘Muniye Nanmugane’ mentions the journey to Sri Vaikuntam.