Some scholars say that you should raise your hands when you stand up as Sheikh Bin Bazz and Ibn Othaimeen say. Others, such as Sheikh AL Albani say you should do it while you are sitting down and before you stand up as this was reported by Ibn Omer.
I don’t have any solid proof on this issue but I do it when I stand up and I believe that both are acceptable, though the first is more practiced by Muslims.
And Allah knows best