title: Turning column into POSIXct date/time series
body: <p>I am trying to reconfigure a column in my data frame (str = 'character') that has the format: 'MM/DD/YYYY HH:MM:SS' into a date/time series column (str = POSIXct) for use with the rmweather package. </p>
  
  <pre><code>&gt; DNO2$`Date &amp; Time`
      `Date &amp; Time`
      &lt;dttm&gt;  
  [1] "31/12/2017 24:00" 
  [2] "01/01/2018 01:00"
  [3] "01/01/2018 02:00" 
  [4] "01/01/2018 03:00"
  [5] "01/01/2018 04:00" 
  [6] "01/01/2018 05:00"
  </code></pre>
  
  <p>In brief, I want to go from: 
  'MM/DD/YYYY HH:MM:SS'
  to: 
  'YYYY-MM-DD HH:MM:SS'</p>
  
  <p>I've tried using the <code>as_datetime()</code> function in the <code>lubridate</code> package to do this, but I receive a strange output:</p>
  
  <pre><code>&gt; DNO_18$`Date &amp; Time` &lt;- as_datetime(DNO_18$`Date &amp; Time`, tz="Europe/London")
  &gt; head(DNO_18)
  # A tibble: 6 x 8
    `Date &amp; Time`       Rathmines Ringsend `St John`
    &lt;dttm&gt;              &lt;chr&gt;     &lt;chr&gt;    &lt;chr&gt;           
  1 2031-12-20 17:24:00 0.299999… 0.90000… NoData          
  2 2001-01-20 18:01:00 0.299999… 0.80000… NoData          
  3 2001-01-20 18:02:00 0.299999… 0.90000… NoData          
  4 2001-01-20 18:03:00 0.100000… 0.80000… NoData          
  5 2001-01-20 18:04:00 0.200000… 1        NoData          
  6 2001-01-20 18:05:00 0.200000… 0.90000… NoData    
  </code></pre>
  
  <p>Any help with this would be appreciated. </p>