When I did it I was told I could do either, the factors that made me go for it in one go were:
1) One attempt was slightly less time in the a/c than doing 2 separate runs.
2) availability of examiner, does he mind splitting in 2. Mine said not if onto different days but then he couldnt make 2nd date I had in mind so ended up going for 1
AND, in the end, it wasn't that bad...it was a long flight but you're not going to fall asleep at the wheel (yoke? ..Stick?) doing it.