Answering your question whether the Preserved Tablet reaches beyond the Last Day.
You already cite the most important source
He said: Write what was decreed about everything till the Last Hour comes.
The Preserved Tablet ends with the Last Hour. The decree ends with the Last Hour:
Sunan Abi Dawud Hadith 4708 (EN:4691)
One of you will do the deeds of those who go to Paradise so that there
will be only a cubit between him and it or will be within a cubit,
then what is decreed will overcome him so that he will do the deeds of
those who go to Hell and will enter it; and one of you will do the
deeds of those who go to hell, so that there will be only a cubit
between him and it or will be within a cubit, then what is decreed
will overcome him, so that he will do the deeds of those who go to
Paradise and will enter it.
From the Quran, the Bible and the Sunna Hadith, I have not found any indication that the "time" after the Last Hour has been decreed. In fact, the term of the "Last Hour" implies that time will no more be thereafter. Pre-Quran revelation explicitly speaks that the Book of Life will be opened on the Last Day. The earliest source is the Book o Henoch (c. 200 BC, Jewish book of revelation, not in the Bible)
- Henoch 47:3
In those days I saw the Head of Days when He seated himself upon the
throne of His glory, And the books of the living were opened before
Him: And all His host which is in heaven above and His counselors
stood before Him.
Revelation of John 20:15 (c. 90 A.D, last book of the Christian Bible)
And I saw the dead, great and small, standing before the throne, and
books were opened. Also another book was opened, which is the book of
life. And the dead were judged by what was written in the books, by
what they had done.
So according to all revelation, the Preserved Tablet reaches until the Last Day.
P.S. I found the most explicit indications in Hadith and less reputed Jewish and Christian sources; the Quran, and the Gospel contain some less explicit indications. The Holy Quran mentions the tablets but not the way to answer your question:
And We inscribed for him in the Tablets all kinds of enlightenments,
and decisive explanation of all things. “Hold fast to them, and exhort
your people to adopt the best of them. I will show you the fate of the