People would trade stocks with each other in between those hour intervals. It’d become another after hours trading. It might cut down on the change rate though since it’d make high frequency trading more annoying and cumbersome.
But slowing the refresh rate of trading I think would also make it take longer for stocks to settle after a shock. I think the limited trading windows is one of the things driving Bitcoins volatility? Increasing the time between when something happens and when the effect is felt would decrease the damping on the system.
Edit: sorry I missed the eli5, this is not a super simple answer