I'm still wrapping my head around this.
So basically the premise is if a stock had large (10%+) intraday movement yesterday and hasn't yet reverted back in line with the rest of its sector by the next market close, place a bet that it will revert during the following night (night #2)?
It doesn't look find_cointegrated_pairs() finds stocks cointegrated specifically with the 10%+ intraday movement stocks. Instead, it looks like when you run find_cointegrated_pairs(sector_df) it simply creates a list of all the cointegrated pairs in those stocks' sectors. It doesn't seem like this would even necessarily contain pairs cointegrated with the stock in question. If this is indeed what you intend, it doesn't seem like you need to run this function redundantly for each stock -- it's enough to run it once for each sector.