The times quoted in most HPF notes are based on times given in a number of authoritative sources.
From the feedback we receive from the exams it would appear that the examiner tends to go for slightly longer times.
For 35,000ft we give 15 to 30 seconds. Of the four choices offered 5 minutes is far too long and 3 and 12 seconds are both too short for a seated pilot (implying no physical exertion).
That leaves 45 seconds as the best of the four choices.