No, you've mixed it up slightly. Basically, the Sejm already passed the law, but the Senate threw the law out. As a result, it has to return to the Sejm so that the Senate's amendment (i.e. binning it) can be considered. The Sejm can choose to accept or reject the amendments made by the Sejm, or it can be placed in the legislative freezer if the Marshal doesn't choose to bring it to the Sejm.
So, what's happening right now is that the formal documentation has to be delivered to the Sejm by 23:00. The Sejm cannot consider the Senate's amendments until the paperwork has been filed, so the clock is still ticking. If it doesn't get delivered by 23:00, it will be automatically deemed that the Senate had no position (due to the requirement for the Senate to make a decision within 30 days, otherwise the law is automatically considered to have passed the Senate without amendment). However, the plan is that the Senate will deliver the documentation as soon as the three MP's taking part in tonight's debate have arrived in the Sejm - the two buildings are next to each other. That should take place in the next 10 minutes or so.
Once the documents are delivered, PiS can bring it to a vote at any time. However, they need to be able to win the vote - from a technical point of view, they also need to have a quorum (so at least half the MP's need to be logged into the voting system). If they attempt a snap vote, it'll be enough for the opposition to simply not log into the system alongside at least 6 from the ruling coalition. So, PiS are unlikely to put it to a vote unless they know they've got 231. As far as I'm aware, there's no tie-breaker - 230/230 results in the bill not being accepted.
One nuclear option that PiS have is to refuse to accept the documentation, but this would almost certainly be a coup d'etat. PiS are unlikely to have the strength to succeed with such a move, and it would without doubt trigger an immediate vote of no confidence in the Marshal and the government.
Looks like JK may have over played his hand.
I think it's becoming clear that he thought that he could pull this off, but he clearly didn't anticipate just how difficult it was to organise. For that reason, I'm convinced they'll announce tomorrow/on Friday that the new election date is May 23rd, and then they'll try and win a vote on postal voting.
The big question is what happens if they lose the vote on postal voting. The choices are that Duda resigns or a state of emergency is declared. Neither is a good option from the point of view of PiS - economic reality will hurt them badly by then.
Update: Kaczyński gave up. Elections in August.