While I have seen many comments on the elasticity of experienced time, this is the first one connecting its length or shortness with whether the time is spent doing or thinking.

I can’t immediately see the correlation, as it would surely depend on what it is you are doing and about what you are thinking.

‘When a man has reached the age of thirty, as Orlando now had, time when he is thinking becomes inordinately long; time when he is doing becomes inordinately short.’

Source: Virginia Woolf, Orlando: A Biography, ed. with an introduction by Rachel Bowlby (Oxford: World’s Classics, 1992), p. 95

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