My 8 year old niece and I rode it several times during our June trip and here is our assessment of intensity highest to lowest:
Night time, back of train
Day time, back of train
Night time, front of train
Day time, front of train
I think where you sit is much more important than time of day if you are worried about kids. We rode in the very front and when they finally stopped braking the train and let it go down the hill, the front car is already 1/3 to 1/2 way down the hill. Terribly boring for older kids but great for those intimidated by roller coasters because there is no stomach drop.
Towards the back of the train is great, though, and it is so much more intense at night!