It is intentional. They've tried in the past to make the pass take longer. This is just the latest attempt to do so.
We've converted general objectives for some missions based on the average 30 minute PvP Summoner's Rift game.
Riot knows the average game time is less than 30 minutes. This change is just to make people play longer for the same rewards. Their goal is to make the progress slower without most people noticing (greatly reducing the speed for players who played ARAM/Featured/TFT/vs AI.)
Nope, we're tuning it from actual data. There should be NO CHANGE whatsoever for the vast majority of our players.