I will post a few things that I have personally seen to be effective. This involves spray paint..if you can find a route..either straight or out and back..mark the street..modestly..not tagger graffiti style,mark the starting line,the turn around..usually 10k is a good start..marking every kilometer is not critical but it can help. You start to divide the course into time split sections. Depending on your experience and fitness 99% of most racers find out you get too jacked at the beginning and go out too fast..I have seen people close to anaerobic before or right after rolling out..in any type of racing that is almost always wasted calories -watts.
once you get some baseline times, you can start to make specific improvements..finding places of mistakes..drinking,shifting,standing,sitting in the wrong place at the wrong time..costing time and energy. The big,huge advantage of TT training is the clock..it's absolute..unlike a crit or road race were the winning time is relative..in a TT against yourself,you always lose unless you best your time. But that doesn't mean that is good, but consistent fast times and the post effort feelings you have can really really indicate your fitness and readiness..
Group riding is much easier because you only need to respond to relative pain and in my experience,it's way way easier to be motivated in a group,of other racers,and or friends.. Punishing yourself is difficult,but it's super important about the depth of your ability and training results.
In my experience I have seen really good racers, road specialists, get a rude surprise from accomplished mountain bike racers, cross country runners,swimmers or snow shoers that mostly suffer alone and know how to push themselves wo cheerleading or other outside motivation..
You see it in high level racers of all types..either they have an extra gene, or are missing the gene that signals pain..if you can successfully train yourself in TTs to ignore or enjoy pain it crosses over into mass start events..
Couple of books out there w titles similar...Time Crunched Bike Racer..or similar..
Also some online resources about TT improvements
Good luck