Doom Speedruns are based off the in game onscreen timer which doesn't include milliseconds, and thus they are not counted (All times are rounded down to the second)

On current dsda you can see now that there are 2 tipes of "records". "First to break second barrier" - basically main timing method, as used here aswell. "Record" sometimes can be same second but less game tics. Widely accepted is the fact of getting the Second, not the Tick, so miliseconds matter, but also kinda don't to some people.