The iracing UI being what it is, it’s quite difficult to put into words 😄
From the website, if you click the big green race button you’ll get the option of filtering for time trials, which will give you a list of servers ready to go in the next few minutes (which is weird because it’s always been solo for me).
You’ll never have to wait more than a couple of minutes to spin the server up. Generally a couple more minutes to actually get in.
From the new iracing UI, when you kick off a race there’s a button that says solo race. Somewhat counterintuitively, if you click that, a little menu pops up with Time Trial in it.
It’s a bloody awful piece of UX design whichever one you use.
Both ways do the same thing although I can’t seem to get VR time trials working with the new UI so I kick those off via the web.