After applying the mupirocin ointment to the affected area you should start seeing results and the mupirocin ointment should begin to work within a day or two.
As long as you keep applying the mupirocin ointment everyday then you should see full results within 3 to 5 days.
If you do not see an improvement after 5 days of using the mupirocin ointment then you should speak with the doctor about it.
Your skin infection could need further treatment or a stronger ointment than the mupirocin ointment can provide.
So keep applying the ointment daily for 5 days or more and if you do not see a significant improvement within 5 days then a doctor should take a look at the skin infection.