Need to speed up Spreadsheet

JWorthers 

Adding a macro to this large workbook is putting a bandage on a big problem and introducing a security element where it's not needed.

The way to best optimize this is to reduce the number of inputs.  The workbook posted is slow because it has a ton of scalar-based based formulas (1 cell = 1 formula).  This adds up quickly with 900,000 rows.

These are the formulas I've added.

The intervals column repeated:

=TOCOL(times*SEQUENCE(,37866,1,0),,1)

The KW column in sheet2.  The '2' in the XLOOKUP is for binary search (ascending).  Since your times are in ascending order, we can speed up the search a bit with a binary search.

=XLOOKUP(B5#,times,Sheet1!F9#,,,2)

The 'Higher/Lower' column:

=LET(
    a, DROP(C5#, -1),
    b, DROP(C5#, 1),
    IF(a > b, "Higher", "Lower")
)

The final column - I call it 'status':

=LET(
    counter, SEQUENCE(ROWS(D5#)),
    MAP(
        counter,
        D5#,
        LAMBDA(c, d,
            LET(
                status, IFERROR(TEXTJOIN("-", , CHOOSEROWS(D5#, c, c + 1)), ""),
                SWITCH(
                    status,
                    "Higher-Higher", "Really High",
                    "Higher-Lower", "Higher",
                    "Lower-Lower", "Really Low",
                    "Lower-Higher", "Lower",
                    d
                )
            )
        )
    )
)

The workbook is now an XLSX - 20 MB.