The +10 is you can book up to 10 days of ADR's past your check in date.
If June 24 is your 180 day window for a Dec 21 check in date, you can make all your ADR's on the 24th for Dec 21 thru Dec 31 (10 days) instead of calling each days 180 window.
I hope this makes sense, I just wrote it, and Im not sure if it makes sense to me.
Not at 180 days if your stay is over 10 days. At 180 days before check-in, you can book up to 10 days of your stay. I'm not sure when you could book days 11 and after, if you have to wait until 180 days from that date.