title: Convert datetime from Excel to R
body: <p>I read an excel file with <code>library(readxl)</code></p>
  
  <p>In excel I have format: <code>9/14/2017  7:58:58 AM</code> in R it ends up <code>42992.332615740743</code>. How can I bring back to human readable format in R?</p>
  
  <p>Do I need supply <code>origin</code> for <code>as.POSIXct</code>? What is the <code>origin</code>?</p>