Time is short — I cannot speak with you at length.
Tips
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Strongly literary/formal. Used in business apologies, formal invitations, classical Chinese, and (importantly) in official RSVP language: 因事不克出席 ('unable to attend due to a prior matter'). Modern colloquial equivalent: 不能 (bùnéng).
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克 (kè) here carries its classical meaning 'to be able to / to succeed in' (also seen in 克服 kèfú 'to overcome' and 克勤克俭 kèqín kèjiǎn 'able to be diligent and frugal'). 不克 = 'not able to' — preserved unchanged from Classical Chinese.
