> They say that stocks go down during the day and up at night

There are lots of things "they say" about the markets, "sell in May and go away" is another famous one.

Most of it pure BS, some of it is half-true, and the rest are sayings that date back to the "good old days" pre-HFT, Hedge Funds and leveraged trading.

Frankly "stocks go up at night" is a ludicrous proposition.

Feel free to give it a go, but corporate actions, corporate RNS, world events ....."events dear boy, events" will very happily shit on you from a great height if you think you're going to make money through short-term overnight holding.

"Time in the market is better than timing the market" is about the only true saying that remains.