Update. Ran my first TT yesterday. SD Time Trial-Merckx Class. Training up for the event was not terribly structured. Mostly base miles and some interval training (un-coached) once or twice a week.
I ran my fixed and did OK. As in OK, I mean that I finished last but the spread in times was pretty even, and I was not a piece of "data scatter" falling way off the back. Successful in that I hit it just hard enough at the start that I had steam left to finish strong. I had hoped to average over 20 mph, and just missed it.
I turned the Garmin over so I couldn’t see it, forcing myself to go by feel. After, when I dismounted I had a lot of burn in my glutes, the first time I had ever worked them that hard.
I was slow, but as a learning experience I call it a success. I learned what a comfortable 20k pace was, and that I can go a little harder next time. I got data, burning glutes, which indicates I need to learn more about core training. I did find a good stretch for the glutes.