Multiple sources say that existing Twitter shareholders have until 5pm today to lock in their IPO share plans, which fits our earlier reporting that an S-1 registration will be publicly available by the end of this week. Possibly tomorrow, but more likely on Friday.

Once the filing is made publicly-available, Twitter must wait exactly three weeks before beginning its “road-show” for prospective investors. So it probably would kick off on Monday, October 28. At that point, Twitter has two choices: Either do a truncated road-show that lets it price that Thursday night (i.e., Halloween — thus earning the scorn of us reporters with kids), or do a full-fledged process that would take it until the following Thursday night (thus beginning to actually trade on November 8).

My initial assumption was that it would choose the former, given that Twitter’s road-show is really more about allocation than finding buyers (particularly since the float is expected to be small). But those familiar with public offerings suggest that the latter is more likely. As one of them put it: “Why risk ticking off all the investors in Baltimore or Denver? You may need them one day.”

So November 8 at the latest. Just in time for those who want a jump-start on the holiday shopping season…

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