Is it supposed to separate immediately from the base solution or am I doing something wrong?

it starts to separate immediately and it takes about 10 minutes to finish ime, though many teks say to wait at least 15 minutes to be sure.
(I always use 100g of mhrb at a time though)

In my experience, within the first 5 min the vast majority of it has separated. Say 90%. Another 5 min and its finished separating. Giving the container a few knocks on the side helps the last 10% separate.

it separated immediately which I thought was kind of weird.
I used white spirit instead of naphtha btw