Approximate time to execute algorithm
If an algorithm is $O(\log n)$, then you can conclude absolutely nothing about the running time of the algorithm. This is due to many factors, one of which is that $O(\log n)$ hides an arbitrary constant factor: both $\log n$ and $100\log n$ are $O(\log n)$ (not to mention functions such as $10^6\log\log n + 10^{15}$). There are also other reasons, but this reason is probably enough.