Cheques used to take up to 5 days at one time,but that seems to be down to 3 working days now;but new laws are making it quicker.
If we assume that you paid the cheque in today (Tuesday) then if the person wishes to stop the cheque,they woud probably have to do so by Friday at the latest.
However,I am assuming this to be the correct clearance period.
If the person who gave you the cheque put their Cheque Guarantee Card Number on the back, they CANNOT stop the cheques as this constitutes fraud.
I hope someone else who has more banking experience can add to this (or correct it).