得闲 is a verb‑object compound meaning 'to have free time' or 'to be at leisure'. As a separable verb (离合词), you can insert elements between 得 and 闲, e.g. 得半日闲 ('get half a day free'), 得不了闲 ('can't get any free time'). It is often used in polite, written Chinese — especially in letters — to convey 'at your leisure' or 'when you have a moment'.