Hurt lower back, how long to recooperate?

So I purchased my first kettlebell, 16 kg, Mar 1 and mostly learned by watching Pavel’s "enter the kettlebell" dvd and attending 2 local classes. Last Thursday I attended my first class taught by an RKC trainer, Fawn Friday, with slightly heavier bells, (20 kg for snatch, press, 24 kg for swings) and the intensity was close to murder, (I’m in good shape but that class wiped me to the bone).

The next day I noticed a slight pain in the small of my back, on the left side, when I did swings. I took a few days off, switched to tactical pushups, plank and overheads, and my back felt better after a few days. I tried running for the last 2 days and found that this causes no pain.

I tried swings again thinking it was safe and after a few min the back pain returns.

So I am back to my alternative kettlebell routine and running until my back is at 100% but I was hoping to get some advice from veteran gireviks.

How long should one recooperate from such an injury? A week? 2? I don’t want to patiently wait 90% of the correct time, then try swings again and re-injure myself and have to start over again.

Any advice?