Not sure I understand the "qualifying time" aspect. Does hitting 2:55 guarantee you entry into the Boston Marathon, whereas achieving the "cutoff time" gets you into the lottery for one of the remaining spots?
But it actually doesn't guarantee you entry because for that age group (Male 18 - 30?) there ends up being too many qualified entrants so they have to shave down the actual time required for entry.
When I was running, it was 3:05 for example but you had to run a <3:03 to make it in.
How do these runners get into the race if they needed to go 3:03:00 (or whatever the current number is) to qualify? I'm clearly missing some piece of important information!
If you ran a marathon sufficiently fast to get under the qualifying time, that doesn't mean that you are required to run THAT FAST on race day for the Boston Marathon.
Some runners try and run fast on race day and discover that their body has hit the "wall" and are forced to run slower, walk for much of the remainder of the race, or worst case, drop out.
Qualifying times for the Boston Marathon are different for older age groups. Older runners can get into Boston with a much slower time than someone in their 20s.
Then there are years where it would require super-human effort to get close to a qualifying time (i.e. 2018, year of heavy rain and wind, see https://runningmagazine.ca/sections/runs-races/japans-kawauc... )