Speed accuracy- how accurate is accurate?

It is all about enjoyment. Wow / flutter is more important in my mind than absolute pitch. 

Question is, how much effort are you willing to put in and whether it will be worth it. :-)

The table is rock steady- how much effort am I will to put in? Considering everything sounds right, not much 

There is your answer. :) But mathematically, it is off by 0.6% of perfect. That's pretty good. 

By most accounts, the iPhone method is not the most accurate way to measure platter speed, but it puts you in the ballpark. So I would not conclude that the speed error of your turntable amounts to the difference between what you measured and 33.33 RPM. It might be more, or it might be less.