"Leth uair an dèidh còig."
Translation:Half past five.
My view would be not at all. Firstly it does not help you understand the Gaelic structure at all, and secondly, because there are so many bilingual people, I think we can be fairly certain that most of them would use the corresponding structures in Gaelic and English in the same contexts.
Me neither. But since you mentioned specifically about the Gaelic structure versus "thirty minutes", I thought there might be some pre-modern-clock concept of marking time. HIstorically, people were measuring in dozens, scores, and there is nothing wrong in it. For instance, we measure time of smoking cigars in thirds (cigars, not hours, though), and I find it very convenient.