Competing answers are central to StackExchange;Stack Exchange; the highest voted one being the one that the community thinks is "best". With that said, I'd consider flagging when the duplicate is posted days or weeks after the original AnswerAnswer.
At present there are the following options:you have the following choices:
- Do nothing.
- Leave a comment.
- Vote the duplicate answer down - difficult as technically it is useful (assuming that the answer is correct).
- Flag the answer for moderator attentionmoderator attention.
Two people posting competing answers at the same time and editing them to make them better is not a problem as this is the gamification of StackExchange.