Determining Gaps between Dates

Bifinity_75 Anonymous Thank you for your responses.  After diving deeper into my data, it turns out there are some other factors to consider.  Initially, I wasn't aware that a room could be occupied by more than one item at a time so some of the calculations based on "EARLIER" or utilzing the Index column in Power Query were resulting in some incorrect dates.  Here's a better indication of what I'm working with:

As you can see, some of the blue bars overlap and they are in the same room at the same time.  The green highlights are the gaps in the rooms for this time period that I'd like to be able to show. The point of all of this is for an individual to be able to look at a Gantt chart and say "OK, this room is available from this date to this date".  
Another consideration:
 - A gap of only one day is irrelevant so it would not need to show up on the Gantt

Hopefully this helps and I really do appreciate your effort here! 

Regards