title: Pandas Dataframe subtracting float value from a column
body: <p>Is there a way to subtract a constant value from the whole column?</p>
  <p>If my dataframe is</p>
  <p><a href="https://i.stack.imgur.com/SM2Dt.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/SM2Dt.png" alt="enter image description here" /></a></p>
  <p>I want to subtract 2.5 from column 1 so that it appears as</p>
  <p><a href="https://i.stack.imgur.com/oruJh.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/oruJh.png" alt="enter image description here" /></a></p>
  <p>Also, is it possible to convert Date+Time into minutes?</p>
  <p>Thank you!</p>