City took the lead through Cole Palmer in the 77th minute, but Leandro Trossard made it 1-1 in the 11th minute of added time after his shot deflected off Manuel Akanji.
Referee Stuart Attwell initially indicated an additional eight minutes at the end of the game, but it was extended further due to a clash of heads in that period involving Kyle Walker and Thomas Partey.
In an effort to clamp down on time-wasting, referees have been instructed to add on more time for any in-game delays.
Guardiola, speaking after the game, said the alterations could have a profound effect on matches.
He said: “It is not annoying; we have to get used to it. I had the feeling, not because we were winning 1-0, it was just the fact I had the feeling that much didn’t happen to extend by eight minutes
“But it is a good question for the [rule-making International Football Association Board] and all the people because they don’t consult the managers; they don’t consult the players.
“Whatever their opinion, we have to accept it. Now the games will be 100 minutes, that’s for sure.”
