As the freshly sulfided catalyst is hyperactive. The cracked stack contains high concentrations of olefins, diolefins and aromatics which are hydrogen deficient. In the presence of Hydrogen, reactions rates can be very fast consuming more hydrogen. High consumption of hydrogen will lead to localized starvation of hydrogen and hence at the end coke formation at the catalyst.
So it is better, not to introduce cracked stock at least within the first three days.
But there are some chemicals in the market like Acticat Shield which can reduce the hyperactivity of the catalyst by providing protective layer. Further details can be found at https://www.porocel.com/71-acticatshield/
Hydrotreating Process Engineer