4. How many years would it realistically take to do mostly day flying?
You could do daytime flying within a year in right seat if you bid for more junior equipment and bid RB (afternoon call). If you want a line and flying days, a long time.

I will also add, that if you are willing take a risk and drop most of a junior night flying line (if it will let you, depending on seat), hawk open time, and check the sick calls every morning when they drop, you can turn a mostly night flying line into all day flying.