title: JQuery UI DatePicker using 2 date fields trying to get date difference
body: <p>I have 2 JQuery Date fields </p>
  
  <ol>
  <li>Arrival</li>
  <li>Departure</li>
  </ol>
  
  <p>Arrival date must not be todays date - i got this sorted using minDate: 1 in the javascript</p>
  
  <p>The Departure date must always be a minimum of 2 days ahead of arrival date. i thought minDate: 3 would work but thats querying off of todays date. it works fine if the user picks tomorrows date in the arrival field but if the user picks an arrival date in the future it breaks. I need the departure date to reference the arrival date and move it 2 days ahead as the minimum date the user can pick, essentially when booking this hotel the user can not stay for one night, 2 night min is required.</p>
  
  <p>finally i also need to calculate the number of nights between the arrival date and departure date into a 3rd text field. so when the departure date is entered it automatically inputs number of nights in 3rd text field. I also need it to work in reverse, if a user decides to put in number of nights i need the departure date to change accordingly.</p>