That's exactly how I understand it, minus those delta numbers being readily available. Thanks for filling in that gap in my knowledge!
Looks like the delta of the $800s was 12% @ market close, meaning that to delta hedge appropriately for the 7,647 outstanding contracts, MMs needed to hold 764,700 * .12 = 91,764 shares to be delta neutral for just these contracts. This assumes all contracts were sold by MMs, and they all delta hedge 100% all the time.
Considering the SP moved up $30 in AH trading, I'd imagine the delta would now be 27% (delta of $770s upon market close), and so the MMs will need an additional 764,700 * .15 = 114,705 shares to stay delta neutral on just these $800 CALL option contracts expiring this week.
But this is just one tiny piece of the puzzle. Their delta hedging requirements will have changed further from not just all the other CALL options they're holding, but also the PUT options. For every sold PUT option, a MM has to be short a certain # of shares to stay delta neutral, but whenever the SP goes up, it will buy shares to unload some of this short position.
Add these delta hedging needs for every single currently outstanding CALL and PUT option, and you can imagine the buying and selling MMs do when the SP moves up and down is enormous.
@ReflexFunds used to calculate the exact numbers. In
this post he calculated that in mid-December for every $10 TSLA SP moved up, MMs had to buy 4.3M shares to stay delta neutral, which might not be 100% accurate, but it's pretty crazy nonetheless.