Wot he above says.
There was a bunch of us planning a group perm on it last year that obviously didn't happen.
That plan involved starting in Crianlarich or the next village west erm... Tynrum, the local shop claims to open at 7am; that gives you enough of a head start on the hoards driving out of the Central Belt and Middle East to get onto the peninsulas, and unless you're quick should get you into Fort Bill around time for them to have either gone home or settled down for the night.
It also gives a midway stop and you can time your return up Glen Ogle to be after the eejits have gone home for the weekend too.
https://ridewithgps.com/routes/31921937Really what you have to be willing to do is sit out the rush if you find yourself in it, doing it as mapped there also means once you're off the A85 on the way South on Day 2 you've got a decent selection of quieter roads for most of the day (negative split territory) and then Pop out at Lix Toll just as it's getting quiet for a full value blast along to Tyndrum when it's emptier, also get to use what you've booked accommodation wise all 3 nights...
Substituting the Fife leg for an East Highlands and/or Strathmore leg is another option, but then it wouldn't be the Twilight would it
Another option is to do it mid-week outwith the holiday season, yeah it'll be dark and cold, but so what.