taken from this link -
https://www.reddit.com/r/ACCompetiz...ntroduction_to_the_blancpain_gt_series_rules/
Race Formats
Sprint Race Weekend
Sprint Races are short time-based races that originally consist of two 1-hour races. It includes Free Practice 1, Free Practice 2 and Qualifying sessions. Each Free Practice session can last up to 90 minutes.
The Qualifying session is split into 2 parts (Q1 and Q2), and can last up to 60 minutes. Two drivers take part in both race sessions, with each driver participating in their corresponding Qualifying split (Driver 1 in Q1 and Driver 2 in Q2). The grid of Race 1 will be drawn up according to the results of Q1, while the grid of Race 2 will be drawn up according to the results of Q2.
Driver 1 will take the start of Race 1, while Driver 2 will take the start of Race 2.
In each race, there is a mandatory 10-minute pit window for changing drivers and tyres. No refuelling is allowed.
The mandatory pitstop is only considered complete if it included a driver swap as well as a complete tyre change.
3-Hour Endurance Weekend
The 3H Endurance race is a time-based race that originally lasts for 3 hours. It includes Free Practice, Pre-Qualifying and Qualifying sessions. Free Practice and Pre-Qualifying can last up to 90 minutes, and it is possible to modify the setup in both these sessions.
Qualifying is split into 3 parts (Q1, Q2, Q3), and can last up to 60 minutes. Minimum 2 and maximum 3 different drivers will drive the same car, with each participating in their corresponding Qualifying split (Driver 1 in Q1, Driver 2 in Q2, Driver 3 in Q3).
The resulting overall qualifying time will consist of the combined average time achieved by the drivers in Q1, Q2 and Q3. Depending on the number of splits completed, the qualified car will be marked with a QR number. QR=1 signalling that each split (Q1, Q2, Q3) were attended; while QR=2, 3, 4 marking 2, 1 or 0 qualifying split(s) attended, respectively. The results of the Qualifying session are determined first by the QR and then by the average time set by each car.
During the race, no single stint may exceed 65 minutes.
Two full-service pit stops are mandated where all four tyres must be replaced and the car must be refuelled.
6-Hour Endurance Weekend
The 6H Endurance race is a time-based race that originally lasts for 6 hours. It includes Free Practice, Pre-Qualifying and Qualifying sessions. Free Practice and Pre-Qualifying can last up to 90 minutes, and it is possible to modify the setup in both these sessions.
Qualifying is split into 3 parts (Q1, Q2, Q3), and can last up to 60 minutes. Minimum 2 and maximum 3 different drivers will drive the same car, with each participating in their corresponding Qualifying split (Driver 1 in Q1, Driver 2 in Q2, Driver 3 in Q3).
The resulting overall qualifying time will consist of the combined average time achieved by the drivers in Q1, Q2 and Q3. Depending on the number of splits completed, the qualified car will be marked with a QR number. QR=1 signalling that each split (Q1, Q2, Q3) were attended; while QR=2, 3, 4 marking 2, 1 or 0 qualifying split(s) attended, respectively. The results of the Qualifying session are determined first by the QR and then by the average time set by each car.
During the race, no single stint may exceed 65 minutes.
Five full-service pit stops are mandated where all four tyres must be replaced and the car must be refuelled.
24-Hour Endurance Weekend
The 24H Endurance race is a time-based race that originally lasts for 24 hours, and is traditionally held at Circuit du Spa Francorchamps. It includes Free Practice, Pre-Qualifying, Qualifying, Superpole and Warmup sessions. Free Practice and Pre-Qualifying can last up to 90 minutes, and it is possible to modify the setup in both these sessions.
Qualifying is split into 4 parts (Q1, Q2, Q3), and can last up to 60 minutes. The top 20 cars according to the combined Qualifying results are eligible for the Superpole session, in which they can complete 2 timed laps to decide the final starting order for the Race. With the exception of the Pro category, where the number of drivers is maximized at 3, minimum 3 and maximum 4 different drivers will drive the same car, with each participating in their corresponding Qualifying split (Driver 1 in Q1, Driver 2 in Q2, Driver 3 in Q3 and Driver 4 in Q4).
Cars competing with only 3 drivers will participate in Q2, Q3 and Q4 only. The resulting overall qualifying time will consist of the combined average time achieved by the drivers in Q1, Q2, Q3 and Q4. Depending on the number of splits completed, the qualified car will be marked with a QR number. QR=1 signalling that each split (Q1, Q2, Q3, Q4) were attended; while QR=2, 3, 4, 5 marking 3, 2, 1 or 0 qualifying split(s) attended, respectively.
The results of the Qualifying session are determined first by the QR and then by the average time set by each car. The Race session is preceded by a 20-minute Warmup session.
During the Race, no single driver stint may exceed 65 minutes.
There are no additional rules related to pitstops, teams are free to change tyres and refuel the car as many times as possible, as long as drivers comply with the 65-minute stint rule.