It depends on context. In the military, for example, it would be "thirteen forty". If someone in everyday life was simply reading a transport timetable, for example, they're more likely to say either "one forty" or "twenty to two".
I would say one forty. (I'm not in the habit of saying a quarter till two or some such, but if it's five till the hour I'll say "It's five till two" or "It's almost two.)
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