A verifier may change its vote for a block several times. Votes are timestamped to prevent replay attacks of old votes.
If a block has a score less than 0, a verifier may vote for it immediately after freezing the previous block. Otherwise, it must wait 2 seconds minimum plus 20 seconds for each point that a block has above 0. So a block with a score of 0 can be voted for after 2 seconds, while a block with a score of 4 can be for after 82 seconds.
If the leading block in a verifier's local tabulation has more than 50% of the vote, the verifier changes its vote to that block if the verifier is allowed to vote for that block based on its score. If the leading block in a verifier's local tabulation does not have more than 50% of the vote, the verifier changes its vote to that block if the verifier was allowed to vote for that block more than 10 seconds ago.
If neither of these conditions is true, the verifier votes for the block with the lowest score if it is allowed to cast a vote based on that block's score. Until such a block exists, the verifier waits to cast a vote.