Millions of people registered to try to get hold of a ticket when the group announced the one-off concert in September.
They were originally asked to play for just 40 minutes but guitarist Jimmy Page insisted that they thought that would be too short a time for them to appear.
Page revealed to Q magazine: "When we were first asked to do this (reunion show), we were asked to play a 40-minute set. We soon realised we couldn't.
"If we go out and play 'No Quarter', 'Moby Dick' and 'Dazed And Confused' with all the solos, you're already talking over an hour."
He added: "We've gone from 75 minutes to 90, to the best part of two hours."
But he claimed that the ageing rockers probably would not be able to perform for any longer, saying: "There's no way I can take on playing three-and-a-half-hour sets now.
"Flying against the wind and the storms, because I just don't have that energy anymore. But I've still got enough in me to get through a two-hour set."