one thing that’s alluded to a few times up there but i think is vitally important, having being involved in and accompanied several failed attempts is not faffing
start as early as you can and keep stops to a minimum, and when you do keep them smooth and efficient, don’t sit down for a nice big lunch for example.
there are also 100 gates along the SDW so stopping at each of them and having a chat/haribo/look at the view (as mountainbikers are want to do) is best avoided, just keep rolling all the time, it doesn’t have to be fast, just always moving, you can save a lot of time this way
echoing most of the above, weather and trail conditions will make the biggest difference, ride what you’re most comfortable on, it’s a long day, and if you can do 100 road miles you can do the SDW, just don’t underestimate it
oh, and don’t go the wrong way in the places everyone goes the wrong way