Fast pours are catastrophes waiting to happen. I have seen formwork for walls buckle and bow multiple times by flowing in concrete faster than they were designed for... The pressure is greater as the aggregate is not locked together and the concrete behaves like a fluid. A very DENSE fluid.
The ties through the concrete snap and nothing is holding the inside and outside forms together. Rut roh!
Slow, even pours placing the concrete in lifts all along the structure while vibrating it with a donkey pecker as you go... that is the best route.
Good luck.
I know about vibrating the casting to take out the air pockets. Do they do this with a fast pour? (I’m an electrical engineer, not a civil). I have seen the results of not vibrating the forms while working on a water treatment plant. All the resulting voids made for a lot of leaks.