On a 3 x 4 closet bend, after installing the 6" length piece through the floor. Later, cut the piece through the floor off, even with the floor. Then my question is, the proper way to install the toilet flange. Do you glue the toilet flange into place and screw it to the floor? By the way it is in concrete. Can you glue the toilet flange into place even with the floor level, before the concrete is poured or is it best to install later??

Before we leave a toilet stub-up and before the floor's poured we put a styrofoam closet wrapper around the pipe so there's room to prime and glue a regular closet flange AFTER the floor's been poured. They can be found at any plumbing shop.
If you poured without the wrapper then you'll have to use a inside flange.
As a rule the flange doesn't need to be screwed to the cement. Good luck, Tom