As we speak. The longer you wait, the greater the risk. Mild chronic infections have a nasty way of becoming severe acute infections at the most inopportune time. The longer you wait, the more tooth damage, the more complex (expensive) the "fix." You need to be on antibiotics to limit stead of infection until Dentist can treat (eliminate) the cause of infection. Please call Dentist NOW.
No time frame. There is no set time frame for sepsis. If you are trying to figure out how long you can wait before going to see a dentist, forget it. Go now. The longer you wait, the worse the problem becomes. After all the pain and suffering and swelling, the result is the same: you will need to see a dentist. So the sooner you go, the better off you will be.
Spreading infection. It depends upon many factors and there is no one good answer. Just be prudent about getting proper treatment in a timely manner!