Raoul Silva makes dental prosthetics. He has approximately $60$ units of WIP inventory at any point in his steady state process, and it takes approximately $255$ hours for each unit to flow through the process $($he often tells customers that the sky will not fall if they have to wait a bit for his high quality$).$ What is the average time in minutes between each unit produced for his steady state process? Go to at least three decimal places for intermediate steps $($so $12\mathrm{.}1786$ would be rounded as $12\mathrm{.}179)$ and one decimal place for your final answer $($so $12\mathrm{.}1793$ would be rounded as $12\mathrm{.}2).$

time between units $($minutes$)$