Disclaimer: I am not a moderator and do not set the standards of what it considered a valid run. This is just my opinion.

A laggy timer in the middle of the run is no issue. Even if the server is lagging, as long as the timer starts and ends at the same ping, the run is legitimate. Cubecraft isn't measuring its timer in ticks, otherwise it would only be in exact multiples of 0.05 seconds (though it does tend to be around these markers since ticks are roughly 0.05 seconds in practice). I'm pretty sure it uses the Date.now() method to figure out the time, so it gets time from outside of minecraft. This means it doesn't matter if there is a lag spike in the middle of the run. I didn't really see any issues with this run regarding the start and ending, at least that were obvious.