SMB is run on 60 frames per second. The most accurate way to officially time the speedrun is to extract the recording of the run, count how many total frames has passed from start to finish, then divide by 60 to determine the time in seconds.

Per darbian (the former WR holder) himself, sometimes he just jumps to keep any potential boredom at bay. Other jumps are from strategies to avoid enemies and hit specific blocks, obviously. Ultimately, there’s no increase in speed on the ground vs the air when going at max running speed.