Highest demand night of the year is NYE. Highest demand week of the year is first week of Dec, followed by Dec 23 to Jan 2, followed by second week of Dec. Highest demand quarter (meaning a time when much at the near park resorts disappears before 7 months out and what is left, if anything, can disappear very quickly once the 7 month window opens): last few days of Sep to Monday after Marathon weekend in Jan; the week that is before the week Thanksgiving is in, the third week of Dec, and time from Jan 4 to the Wednesday before marathon weekend are the only more moderate weeks during that period. Monday after marathon weekend in Jan to last few days of Sep ranges from average to moderate to almost light, and that includes all the holidays during that period. As to lightest times of the year when many things at near park resorts are usually still available well beyond the 7 month window: first two weeks of Feb (e.g., it is now less than 6 months out and much is still open at near park resorts), end of Feb after Princess half marathon, first two weeks of March, last week of April, Sep except last few days.
Hardest rooms at WDW to book which are usually gone at 7 months out even much of the time during that mid-Jan to end of Sep period, in order of most difficult to just difficult: AKV concierge (that can even often be unavailable when booking exactly 11 months out), OKW GVs at the Hospitality House, AKV value and BLT standard, BWV GVs, BWV standard, BWV boardwalk view (don't have enough of a pattern yet for VGF). During that mid-Jan to end of Sep time, BCV studios and BLT Theme Park studios can also sometimes disappear before 7 month out, such as Presidents Day weekend, Princess half marathon weekend, Memorial Day weekend, and the last Star Wars weekend in mid-June.
1BRs tend to last longer than other units (although BLT standard is often an exception where 1BRs may be gone before studios) and can sometimes be available at near park resorts at 7 months out even during the most difficult times of the year. Other than OKW GVs at Hospitality House and BWV GVs, the GVs are usually open at 7 months out except for some times during the the highest demand quarter -- BLT GVs can be gone many days during the quarter; AKV and OKW in mid-Oct, Thanksgiving time, first week of Dec and time around NYE; and SSR first week of Dec and time around NYE. SSR treehouses can disappear before 7 months out Thanksgiving time, first week of Dec, Christmas week, and time during marathon weekend in Jan. Of all the WDW resorts, SSR is usually the last to fill, OKW next to last, and AKV third to last.