They take far more than 30 seconds. The last time I went through one was probably 2 years ago at LHR. You got pulled out of the queue at random.It was optional at the time (go through it or get strip searched) It took about 3 mins but at least you got to jump the queue. Unless the technology has improved a lot then it is still going to take far too long to get everybody going through one.
Spread your legs and put your feet on the dots. raise your arms and put your hands on the yellow dots. Wait a while. Now turn around and do similar. All after you have removed any belongings from yourself.