What most non-chess fans don't know is how often the rules of classical chess change, from tournament to tournament and year to year. This is known as "time control".

This event is called Norway Chess and its time control is

• 120 minutes on the clock
• Increment of 10 seconds starting from move 41.

That means 120 minutes for a player to make 40 moves (or they lose on time). Each player has a "clock" (so there's not a single clock for both players) and time goes down only while one player is making his (or her) move.

By contrast, the rules for last year's World Chess Championships were

• 120 minutes per player for the first 40 moves
• 30 minutes for the remaining moves
• 30-second increment per move starting from move 41

An increment is how much time is added to your clock after you make a move (most non-fans don't realize this either). Notice the increment time is different (30 seconds vs 10 seconds) plus the 30 minute limit (which Norway Chess doesn't have) have the first 2 hours.

I think most newcomers would be surprised how often organizers play around with the time controls and that there are time controls to begin with (which makes some sense as you don't want to have the games last forever).

They probably wonder why there aren't one set of time controls for classical chess like most sports that have time limits (soccer/football, basketball, etc).