With only a few walk-in clinics nearby, Sequoia Family Medical Center may be your best option for immediate care in Porterville. They are open today from 8:00am to 8:00pm, as well as 7 days a week. As long as you visit them during their business hours, you should be able to walk right into 590 W Putnam Ave and be seen relatively quickly. The national average for patients waiting at an urgent care is between 15-30 minutes, so hopefully it shouldn't be too long of a wait.
If you need a 24-hour option, you can always visit the closest emergency room, of course, you will likely pay 3-5 times more and have a much longer wait. In the case of a medical emergency, call 911.