Hello! The yellow number is the time of your fastest completion of a level in frames. (The game runs at 30fps so if it says 60, for example, that means you beat the level in 2 seconds on your fastest attempt)

SoB stands from Sum of Best, which gives you a hypothetical 'best possible time' if you strung all of your best times from each level into one run. (It adds up all of your yellow numbers)

Hope this helps!