Unfortunately you cannot swap the dates from friends or anyone as a matter of fact. Once we reschedule or the date is moved, the system doesn't show it immediately or it takes time(not sure how much time) i think, we have tried this but couldn't see the date for an hour atleast. So please do not try this. If you are trying this, your friend/anyone's dates are also gone.
Keep checking the dates very frequently. They are opening slots for next month ahead and keeping the rest of the days closed/not shown for that particular period of time. They are opening the regular appointments month-by-month basis as far as i observed.