And [so, O Muhammad,] they challenge thee to hasten the coming upon them of [God's] chastisement:62
but God never fails to fulfil His promise - and, behold, in thy Sustainer's sight a day is like a thousand years of your reckoning.63
For an explanation, see 6:57 , 8:32 and 13:6 , as well as the corresponding notes.
I.e., what men conceive of as "time" has no meaning with regard to God, because He is timeless, without beginning and without end, so that "in relation to Him, one day and a thousand years are alike" (Razi). Cf. 70:4 , where in the same sense, a "day" is said to be equal to "fifty thousand years", or the well-authenticated saying of the Prophet' "God says, 'I am Time Absolute (ad-dahr)'."