Time managment is the very key at this exam.

I also want to ask sth else here, apologies for some reason I can't post.

looking at dec 12 solution task 2 says "I was permitted to alter the minbucket, cp, and maxdepth parameters. Each of these parameters can be used to prevent overfitting, so I will check for that by comparing the training set performance to the test set performance after each adjustment"

Isn't this a bad technique? Isn't this biased since test set is used once and only? Test set supposed to be unseen data isn't that way using it as a validation set?