Having got out of Q1 in 13th, Perez was the only driver not to be on track at the end of Q2, and missed out on a final flying lap.
When he was called in, he was told he was in fifth and that there were still four minutes of the session remaining.
After a pause, he said to his engineer: "We finished quite early, no?" and his concern proved to be valid as he subsequently found himself bumped down to 12th - and will start the race in 11th due to Carlos Sainz's grid penalty.
"We had a strategy before qualifying with the team," said the Mexican. "And obviously we don't know this place, and we were thinking what was the best programme, and we went this route.
"Obviously after that, it's easier to know that it was the wrong call. Already in Q1 we were a bit lucky to get through because we didn't get our final lap coming back to the pits.
"And then Q2 just finishing the session a little bit too early meant that there was some evolution still on track, and we were in the pits."
He made it clear that he hadn't expected to finish his session with so much time left on the clock.
"I wasn't aware that much that we were going to finish that early," he said.
Source: Autosport