The information below I have taken directly from the CTT website https://cyclingtimetrials.org.uk/articles/view/9
The minimum age for competitors is 12 years. It is essential that competitors under 18 know the law and the Highway Code, and are competent to ride on public roads alone. They must have the authorisation of their parents to compete.
Time Trial Events
The minimum distance for a time trial is generally 10 miles but shorter races are permitted. Most races are at fixed distances (10, 25, 50 and 100 miles) or fixed time (12 and 24 hours). Riders start at one-minute intervals, or sometimes more, and cover the course alone and without taking pace from other competitors or vehicles. If one competitor is caught by another, the CTT regulations require the overtaken rider to fall back behind the other to a distance where they are getting no shelter or help from the faster rider. At least 50 yards/metres is suggested.
When time trial courses are designed, safety is a major consideration. However, a competitor’s safety remains entirely his or her own responsibility. Events are held on open roads, and competitors must obey the relevant laws and the Highway Code before, during and after a race. Competitors must avoid creating situations that are unsafe for other road users.
There are a number of other points that will help everyone to enjoy safer racing: Cyclists are less visible than most other road users. You should remember this when approaching junctions. To improve visibility from the rear, race numbers are printed on a bright, reflective background. The number must be placed on your shorts from the waistband downwards, and must not be covered by other clothing. Your number cannot be positioned in the middle of your back, as with a runner’s number, because it would then face upwards when you’re in a riding position.
You should avoid doing U-turns in the road, both while warming up for an event, and after you’ve passed the finish. Drivers do not normally expect other road users to make this manoeuvre, which means it can be dangerous. It is CTT policy to eliminate U-turns from courses, and to reduce their use where they cannot be avoided.
You must avoid riding with your head down. Even on a Clearway, cars may stop for a variety of reasons, and the responsibility for avoiding them rests with the rider. In the event of a collision, the fact that the car was contravening the Clearway regulations will not be an excuse. A rider can expect a suspension from competition for any failure to watch where they are going.
Any road junction or roundabout can constitute a hazard in a race. You will often be approaching much faster than drivers expect of a cyclist, which can lead to errors of judgement on their part. Be ready for this. Care is particularly necessary at slip roads joining and leaving dual carriageways and other major roads, due to the long period when a cyclist can be between two lanes of merging traffic or exposed to vehicles leaving the main carriageway at high speed.
If you have an accident during a race, no matter how minor it may seem, you are required to report it to the Event Secretary as soon as possible.
Whatever type of time trial you are entering, club or open, you must be a member of a club that is affiliated to Cycling Time Trials. Being a BCF or CTC member does not generally qualify you to ride time trials unless your BCF Division or CTC District Association is affiliated to CTT.
Entry to club events is usually just “entry on the line” on the day of the event. You will be required to sign a Club Entry Form, and if you’re under 18, you must show the organiser a Parental Consent Form.
Entry to an open event, on the other hand, must be by an official CTT Entry Form, with a closing date that is usually just under two weeks before the event. If the event is over-subscribed, the fastest entrants (assessed on their qualifying times for the relevant distance over the last three seasons) will be accepted, unless otherwise specified. If you are under 18, your parents must sign the Parental Consent Form.
Once your entry has been accepted, you will receive a start sheet a few days before the event giving details of the course, prizes and your starting time. After the race you will receive a result sheet showing where you finished and confirming your official time.
There are some restrictions regarding the equipment that you can use. Brake levers must be positioned so that you can get to them quickly from your normal riding position. Triathlon bars with forearm supports may be used. You can use a solid disc wheel at the rear of your bike, but not on the front. Deep-rimed wheels and composite spoked wheels (eg tri-spokes) may be used in either or both positions. Under no circumstances may streamlining devices be used.
Clothing and Advertising
Time triallists usually wear either a short-sleeved racing jersey and cycling shorts, or an equivalent one-piece suit. Sleeveless tops are not permitted. The wearing of a hard-shell helmet is recommended for all, and is compulsory for juniors.
Whether you are allowed to carry advertising logos depends on the type of event, and on your club. In a club race it’s simple: you can carry any advertising you want. However, in an open event you can carry advertising only if you are a member of a CTT-registered sponsored club, or you are a member of a UCI-registered professional team. Manufacturers’ logos on their products are fine.
Courses are measured to a high degree of accuracy using special equipment. Marshals are appointed to help riders follow the course, but it is still your responsibility to make sure you know the route.
Courses are normally only identified by a code system – this is throwback to the days when races were conducted in secret, and some system was required that would disguise the whereabouts of a race. The course code has an initial letter that identifies the region that the course is in. Then there is normally a distance, and a number for the exact location (though the format varies a bit from region to region). You can look up the code and find a description of where the course is either in the CTT handbook, or on this website.