Hi Caroline,  As I understand it, dexamethasone stays in the circulation for about 18 hours and is therefore generally only taken once daily.  Most specialists recommend  this dose is taken in the morning, as this way it is more likely to mimic circadian rhythm, so I can’t see any reason why you shouldn’t change!  Taking the florinef at the same time also shouldn’t cause any problem either.  Good luck - it sounds as if you are going in the right direction to sorting yourself out!