https://www.gamespot.com/articles/ps4s-spider-man-game-length-confirmed-by-insomniac/1100-6461417/

Insomniac Games community director James Stevenson has revealed PS4's Spider-Man takes about 20 hours to beat. Stevenson unveiled the number when answering an inquisitive player's question on Twitter.

It's worth noting that 20 hours is the average taken from multiple play testers. Stevenson wrote that 20 hours is about how long it takes for someone to beat Spider-Man on the default difficulty and only when completing some quests and activities. Those that do more will take "a lot longer." So the 20 hour mark is for the average player who's not looking to test themselves against the game's most challenging combat or complete every optional objective.