Tamiflu takes from 24 to 48 hours to start working.
For Tamiflu to properly work you need to take the Tamiflu 48 hours before the onset of the flu because it needs at least 48 hours to work to kill off the flu virus before it takes full effect on your body.
If you do take the Tamiflu after you get the flu then it won't work properly so make sure you take the Tamiflu 48 hours before the flu begins for it to work.