How long does the average fever last?

There is no easy answer for this. Some fevers only last an hour or two, others last for days. People with serious infections or cancers or autoimmune diseases can have intermittent fevers for months to years. A classic infectious diseases consultation is the patient with fever of unknown origin or (FUO) most commonly caused by infections, but often by cancers or other diseases. Do you have a specific fever-related question or disease in mind?

1 day or based on how many leaves you want to take

2 hours.
which means you should go to hospital for a severe infection.