Format Pattern is usually the best option to format dates (and times) in JMP (in my opinion). You would do this most of the time interactively in JMP (sometimes this can be a bit annoying to get working or understand how it works though).
Starting point character nominal

Change to Numeric Continuous and change format (do not press Apply or OK yet)

Click set format pattern, set the format provided by @mmarchandFSLR

And then click OK (or apply first).
Next right click on the formatted column and select Copy Columns
New Column("Column 3",
Numeric,
"Continuous",
Format("yyyy-mm-dd", 12),
Input Format("Format Pattern", "<YY><MM><DD>"),
Set Selected
)
Or check enhanced log, this is better option in this case as you are modifying existing column

// Change column info: Column 3
Data Table("Untitled"):Column 3 << Set Data Type(
Numeric,
Format("Format Pattern", "<YY><MM><DD>", 6),
Input Format("Format Pattern", "<YY><MM><DD>"),
Format("yyyy-mm-dd", 12)
) << Set Modeling Type("Continuous");
-Jarmo