Display different time from one field value
Well you are better off writing a custom module or using a function that can swap out a timezone variable instead of manually calculating by adding 8 hours...
But if that's what you want here is one way of achieving this..

Create a node template for that content type or specific node (whichever suits your scenario).

In the template file you can use:

 &lt;?php
    // Your date field. note the appended 'field_' at the start of the machine name.
    $date = new DateTime($content['field_YOUR_FIELD_MACHINE_NAME']['#items'][0]['value']);

    // Boston date field
    $boston_date = $date;
    $boston_date -&gt;modify("+8 hours");
    $boston_date -&gt;format("d.m.Y H:i");

    //Outputs your date field with 8 hours added to it.
    print 'Eventname - starttime for Boston: ' . $boston_date;
 ?&gt;