Hello Colin,
sorry for my prolonged silence!
Dating masks, especially hanpō, is generally not that easy. Very little is written about the subject and most sources simply stating “Edo period” or similar, without further explanations (I know only one comprehensive book dedicated to mengu).
The problem is, that you can find such hanpō in almost identical shape in the early as well as in the late Edo period. The difference is often workmanship among other small details.
However, I dare say early Edo!