Story highlights The Senate majority leader could start debate as early as Tuesday

Republicans have a narrow window before end of year to pass their tax plan

(CNN) As was the case when Republicans' plans to repeal and replace Obamacare reached this stage in the legislative process, congressional observers don't know when exactly senators will vote on the GOP tax plan.

And we likely won't know until, well, it's time for the vote.

On Monday, Sen. John Cornyn, the Senate Republicans' whip, said "Hopefully we will get to the floor on Wednesday." Asked to clarify if he meant the vote to proceed will be Wednesday, he said yes.

The reconciliation process on the floor is one enormous convoluted and confusing time suck. Once Senate Majority Leader Mitch McConnell brings the bill up on the floor, which could happen as soon as Tuesday, the clock starts on 20 hours of debate. But it's not necessarily 20 hours straight -- Democrats can deploy a series of dilatory tactics to stretch that process out quite a bit. And the Senate likely won't stay in session straight through the 20 hours, so when they break, the clock stops.

Once the 20 hours of debate officially comes to an end, then the vote-a-rama starts. This could go for, well, a very long time. Historically, the end of the vote-a-rama would entail a vote on the amended tax bill, then a final vote on the bill. But as with the battle over health care, even this is subject to change. Arizona Republican Sen. John McCain killed that effort in July on an amendment vote earlier than expected.

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