title: What time format is this & how to convert to readable format?
body: <p>This is one of those questions that I'm sure will have a quick answer but I can't seem to find it.</p>
  
  <p>Using the Facebook Graph API, the opening hours for a business are returned in JSON using this format:</p>
  
  <pre><code>"hours": {
    "mon_1_open": 406800,
    "mon_1_close": 437400,
    "tue_1_open": 493200,
    "tue_1_close": 523800,
    "wed_1_open": 579600,
    "wed_1_close": 610200,
    "thu_1_open": 61200,
    "thu_1_close": 91800,
    "fri_1_open": 147600,
    "fri_1_close": 178200,
    "sat_1_open": 237600,
    "sat_1_close": 264600,
    "sun_1_open": 324000,
    "sun_1_close": 345600
  }
  </code></pre>
  
  <p>The hours should be 0900 - 1730 weekdays, 1000-1730 Saturdays &amp; 1000-1600 Sundays.</p>
  
  <p>I can see there are 30600 seconds between opening and closing on weekdays, so it's a number of seconds since something, but I'm not sure since what.</p>
  
  <p>What kind of time format is this, and how can I convert it into something usable in PHP?</p>
  
  <p><em>Bonus: Why would they use a timestamp <strong>"since"</strong> something, seeing as the hours recur weekly?</em></p>