Academic tassel at convocation: left or right for dual undergraduate/post graduate students? Apologies if the question I ask is not suited for this SE.

At convocation, it is usually the culture for undergrads to wear the tassel on right and switch to left after being given the degree. For postgraduates, the tassel is supposed to be on the left.

My question has two parts:

a) What about people who are straight away getting their post graduate degree (in case of students who have opted for a dual degree program or integrated course)? Do they wear the tassel on the right (as they have never been given a degree before)?

b) When exactly should the turning of the tassel happen (for undergrads)? On the stage itself when receiving the degree?

Many thanks for any answers in advance!
At my institution (in the United States), students always wear the tassel on the right, even if they've earned a prior degree.  At Commencement, the President tells the students when to switch.  (In our case, that's everyone at once, after diplomas (really, diploma covers) have been presented.)