i found some facts on the official site
As sole tyre supplier to a field of 66 cars, the TotalEnergies 24 Hours of Spa is a huge undertaking for Pirelli. The Italian company produces up to 17,000 tyres for the race, sending around 35 trucks and a huge army of support staff to the Ardennes.
They provide each car with a maximum of 30 sets of dry tyres, which must be used from free practice onwards. Two sets from the official test day can be carried over as part of the 30-set allocation, while an additional set is authorised for the cars taking part in Super Pole. These can’t be used during the race, so there's no excuse not to push them to the absolute limit.
The maximum length of any stint is 65 minutes, except if a full-course yellow or safety car period is in operation when the stint finishes. In this case, an additional five minutes is permitted to allow the car to get back to the pit lane at a slower pace.
A driver may only complete three full stints in a row. After this, he or she must rest for at least one hour. The maximum driving time permitted over the full race is 14 hours.
Don't quote me because I'm a bit fucked up right now, and endurance racing is difficult to keep up with all the rules across different series, but depending on the situation or strategy, it's not uncommon to double or even triple stint a single set of tyres. Also, I'm not sure if it's allowed or not in this series, but it's normal not to change all 4 tyres every stop but to switch the side that does the hard work.