While true, I think we worry about the possibility of a last-minute vote switch way more often than such a switch is an actual threat.
My previous mode of moderation was to set a hard deadline and say that no votes after that time count. I would change this to say that Day will end at between the hours of 16:00 and 20:00. All votes before 16:00 will certainly count. All votes up to the previously unannounced End of Day will also count. Votes after the surprise end of Day will not count.
Ostensibly, everyone will try to enforce the 16:00 deadline. Any shenanigans would be discouraged since there is an unknown amount of time for the shenanigans to be discovered and countered. In other words, since scum don’t know what end of day is to the precise minute, they can’t coordinate a vote switch without significant risk of getting caught.
My goal would be to eliminate vote-switch-worry, not just vote-switch-shenanigans.