no ofcourse they wont cut marks for you
CIE awards marks on questions, not behaviour. y would they cut your marks if u were late
if they wanted to do something, then it would something like cancelling ur paper or not permitting u into the exam room << these two however are highly unlikely if u were present in the hall the moment the exam started
if u were not present in the hall the moment the exam started, i dont expect them to give u extra time.