I go back and forth on changing your vote.
Arguments for would be learning something new, or breaking information during the period of the vote. For instance, if a news story broke about a politician, or something hidden in the wording of a bill would be highlighted, then one might want to change their vote.
Also, propaganda/information campaigns would ramp up towards the end of the vote, which could be good or bad.
Arguments against are basically logistical burden and opportunity for fraud. It's simpler for one vote, cast in stone.