As a data point, I did a T3-T5 transfer this morning at around 9 am. I went through the fast track connections security at T5 and there was no one ahead of me. On top of that, they were conducting a trial of the new security machines, meaning that (as at my departing airport of HEL) I didn't have to take my laptop etc. out of my bag. To my shock and surprise, I was through security in moments.