This one mention 90 days : https://www.technofino.in/community/threads/redemption-date-of-sbi-vistara-cc-complimentary-flight-ticket.5016/reply?quote=84177
Check here : https://www.technofino.in/community/threads/sbi-vistara-credit-card-welcome-ticket.16576/#post-331045
and https://www.technofino.in/community/threads/club-vistara-the-ultimate-guide-for-indians.20161/
I don't think such a limitation can apply to CV points, although getting refund for flights booked with expired points can be an issue
Suppose just 500 CV points are going to expire next month, then it would mean that you'd have to wait a month till those points expire, to book any later...