title: Calculate available time slots for a bookable resource
body: <p>I have an application showing weekly (Mon-Sun) availability for a bookable resource.</p>
  
  <p>In the view, adjacent to this calendar, the user can choose:<br>
  <strong>A)</strong> Length of desired slot to book (15 min/30min/60min/)<br>
  <strong>B)</strong> Timezone  </p>
  
  <p>Time slots always have the hour stroke as a reference point, i.e. if a user chooses to see 15min slots the possible starting points are only :00, :15, :30, :45.</p>
  
  <p>Let's assume that the calendar internally has an availability between 07:23 and 09:10 tomorrow morning, and taking into account that the user might want to change timezone - what would be the most practical/logical way to manage calculation of available time slots for that time span?</p>