title: R: Convert a Character to a timestamp
body: <p>Currently we are implementing some sort of direct marketing
  We send an SMS (timestamp) on a certain day from a certain country within Europe and then receive a response from a customer in the local country if they are interested in the product</p>
  
  <p>I have a sample data set for two months, of SMS's sent and Responses received (if at all). The end goal is , I want to calculate the time difference in hours between the sent time and the response time factoring in Time Zones and Day Light Savings</p>
  
  <p>The file i received has the time stamps in character format. I wish to convert them to dates of their local timezones, convert them to a standard zone and calculate the hours difference</p>
  
  <p>I have tried the methods below to just create the conversion but it comes back with NA.
  Any help would be greatly appreciated</p>
  
  <pre><code>as.POSIXlt("12/02/2015 11:23", tz = "Europe/London")
  strptime("12/02/2015 11:23", "%d/%m/%Y %h:%m")
  as.Date("12/02/2015 11:23","%d/%m/%y %h:%m")
  </code></pre>