The price changes hands in a blink. The shares and the money take a day.
T+1
Sell your shares on Monday and the cash is not yours to spend until Tuesday. That one day gap is the settlement cycle. The machinery that actually lifts shares out of one demat and drops money into another. Most people never notice it runs until the day the money is late.
Friend sold some shares on Monday morning to free up cash for a deposit. Monday night he pings me, half panicking. Money is not in my bank, did the trade even go through. Nothing went wrong. He had just met the settlement cycle for the first time. The part of the market nobody explains, because it usually runs so fast you never notice it is there.