Currently reading the paper of John M. Griffin and Amin Shams "Manipulation in the VIX?".
My questions has to do with settlement of VIX derivatives (options and futures on VIX). The paper states that the settlement takes place monthly when contracts reach maturity date. This is the time horizon where manipulation could happen because there is an auction in the opening between 7:45 and 8:15 (now 8:20). In this interval traders could increase volume for deep OTM options buy offering bid-prices.
So, what I have not cleared is the mechanism of the settlement. Do the options and futures on VIX expire on the previous day before settlement or it is the same day?