5 days if calpol is helping and no other concerning signs. https://www.nhs.uk/conditions/fever-in-children/
I found this really helpful https://www.nth.nhs.uk/resources/how-to-recognise-if-your-child-is-seriously-ill/
Check the label on the calpol bottle - pretty sure it says to see a doctor if still using it after 3 days.
They usually say a week unless it's very high and not coming down with Calpol x