You know what irks me?
Candlemarks, Fivedays, and Tendays.
I just don't see why "hour" and "week" should be any less exportable than "day", which is only rarely changed. "Month" as "moon-span" or "moonturn" is more forgivable, since that's probably pretty close to where the word came from.
But. Candlemark? Who marks their candles for a specific and consistent duration of time without having a pre-existing word for that amount of time? A word in wide use?
Fivedays? Tendays? Who would use such a word (or phrase) in any conversational context, let alone a formal one? It's cumbersome, it's confusing ("Did he say it would take fivedays, or five days?"), and it doesn't make sense.
Additionally, "hour", "day", "week", "month", and "year" are all monosyllabic words. They can be used quickly without a lot of confusion, and without having to waste all your breath on a single unit of information.