Cast string as datetime

the parsing speed by ~5-10x. originscalar, default ‘unix’Define the reference date. The numeric values would be parsed as number of units (defined by unit) since this reference date. If ‘unix’ (or POSIX) time; origin is set to 1970-01-01. If ‘julian’, unit must be ‘D’, and origin is set to beginning of Julian Calendar. ................
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