Everything I’ve read says take the anti sickness you’re given (whatever is the norm wherever you are) as soon as you get it - because it’s much easier to prevent sickness than to sort it after it starts…
I have an IV of steroids (don’t know which) before chemo infusion then domperidone to take after - my first infusion was quite late in the day so I think the premeds tided me over then I was told to get started on the domperidone first thing the day after so I did as instructed 