I am 36 weeks pregnant and baby's head is 2/5ths engaged. Does this mean that I will have my baby any time soon?

Not necessarily. You are referring to station. Station is a very subjective measurement of how far down the birth canal the baby is. A lower station tends to imply a sooner delivery, but its not a reliable indicator. Different practitioners can measure a different station in the same woman at the same time as well - its more of a gestalt than a reliable objective measure, despite its objective definition.
Please ask your. Health care provider who will be doing your delivery, I have never described engagement in those terms to my pts nor was i taught to use percentages to describe that, a better predictors of that are-are you having a lot of irregular contractions, is the cervix starting to get effaced or dilated and how much effacement and dilitation is there.