I always get up early on Mondays Mondays I always get up early.
In english, we refer to habits usually in the plural.
I would say it either way (American speaker here, which might make a difference). Certainly it's correct with the plural.
American speaker here too. They both sound correct to me, although Monday in the singular sounds more natural and is probably what I would say without giving it much thought.
As an English speaker of English I find both correct, though the plural more natural.
'On Monday I always get up early' This works in English and is more in line with the Hu sentence. Although I'd rather use 'Monday's' here