In calculating the CBOE VIX (post 2014) one has to select near- and next-term options, which are defined as options with >23 days and <37 days to maturity. As time moves on, a currently selected near term option passes the 23 day threshold and the currently selected next-term option takes its place. This is called "rollover".
I am calculating the VIX on a 1-minute intraday frequency. My question is the following: when does the rollover take place:
a) Daily, e.g. for all considered minutes on tuesday, I use a fixed set of near- and next term options. Rollover then takes place at 00:00.
b) Intradaily, e.g. at expiration of the weekly options at 15:00 or 8:30 for 3-weekly options. For minutes on tuesday after expiry, i have to select a new set of options.
The CBOE Whitepaper is not precise on this topic. Tzang, Hung, Wang & Shyu (2010) - Do liquidity and sampling methods matter in constructing volatility indices? Empirical evidence from Taiwan also do not specify.