Assuming an American, Aussie or Kiwi (etc.) presents themselves at the UK border, the landing interview goes perfectly and there's nothing funny about them, about how much time will the officer usually spend checking stuff on the computer?
In other words, how long is it on average from the officer scanning the passport to issuing the entry stamp?
Does it vary between airports (e.g. Heathrow) and seaports (e.g. Calais)?