I found more availability at 56-58 days out than I did at 60. I got what I wanted so I've stopped checking.
One thing: for the days I wanted SDMT FPs, I didn't book any FPs at all until I was able to GET SDMT. I felt like (and I could be wrong), that when I tried to replace an existing FP (say, Peter Pat at 1:50 - 11:50), it only searched for what was available to substitute in THAT PARTICULAR TIME FRAME. That drastically limits what you're looking for.
My strategy was to NOT book ANY FPs for the days when I wanted SDMT. That way, I could search for each person individually, and wasn't limited to a time frame. Ultimately, I found ONE lone FP at a certain time and booked it. Then, I tried to find an overlapping time for the other person in our party. Bingo! I got it.
It's definitely do-able, but due to the strangeness of the ins and outs of FP+, it takes a bit of work.
For sure, keep trying. I'm going Thanksgiving week and was able to find FPs for the 23rd, so it really is possible.