Back in those days clocks weren't as advanced as they are nowadays, hence they played like 10sec per move indefinitely lol. Most of those games weren't even recorded with good reason as classical time control was the only serious way to play chess.
Yea man, the late Gligoric was a legend in the game, but he was even a better person. I loved this quote of his: "I was born a few decades too early, otherwise I would be a millionaire"