What does "it" refer to here? and could you explain about this sentence mean please.
"It" refers to "your work". In English it is common to use pronouns, like "it", to avoid repetition in speech. In this case the sentence is really, "the time you spend prioritizing your work is time you aren't spending doing your work." It means that all the time you use deciding what order to so your work in is time that you could have used simply doing your work.