Answer: Quite a while/almost impossible without DAW (Digital Audio Workstation) software.
Explanation: It's a complicated process, as Rush E uses many notes and chords at the same time as as well as pressing random combinations of keys on a piano which were created on software and also uses more keys than on a regular keyboard as well. You could try and learn the less complicated parts of the song but the parts that are really fast and use more than 20 notes at once will be impossible without software.