User blog comment:DanzxvFan8275/Proposal: President Donald Trump Issues Proposal on Voting Guidelines so he can be Reelected in 2020/@comment-26182781-20170731163157/@comment-33046846-20170731163601

The proposal length was always 3 days. If this passes, the proposer will have the ability to extend it if they want to.

So, extending the time is optional.