Climbing and descending mt Fuji in one day

Hi,
I am planning my trip to Japan and think about climbing mt Fuji on early August. I'd like to know whether it's doable to complete the Yoshida trail, both uphill and downhill (starting from Subaru 5th station obviously) in 1 day, without an overnight lodging in a hut.
My plan is to lodge the night before near Kawaguchiko station and get on one of the early buses to Subaru station. Is there a reason to be worried that the bus will be too crowded so I won't be able to get on it?

If you are in excellent shape and well prepared, it is possible. But it is very tiring and there is a higher risk you will develop a headache due to the the altitude difference or injure yourself due to the tiredness. On sunny days, you will also be constantly exposed to the sun.

Is there a reason to be worried that the bus will be too crowded so I won't be able to get on it?

I don't think that happens.