title: Non convenient date format. Time zone must be defined as "UTC" error message
body: <p>I'm a beginner in programming with R, I have a csv file with 4 columns :</p>
  <pre><code>DateR        P   E    Q
  2017-09-01 0.20 4.6 0.263
  2017-09-02 0.15 3.0 0.157
  ...
  2021-09-01 0.57 8.6 0.574
  </code></pre>
  <p>I want to run a code with a airGRteaching packaging and I have this error message that shows up :
  Non convenient date format. Time zone must be defined as &quot;UTC&quot;</p>
  <p>I had already convert the class of the dataR to POSIXct.</p>
  <p>Please any suggestions ?</p>