[...]I don't think there is anything to do this. Check in the manual. Look up SYSDATE in the index. There is also now a CCYY version, I believe. Maybe there is other new stuff.
SYSDATE-LONG is not a command. It is a special variable, which has a particular value for each run, and is "read-only".
I don't know why you chop up SYSDATE-LONG when you could use it's cousin, SYSDATE. Look around at the descriptions of these in the manual (which you have, and I don't), and see if there is anything new to give you the day of the week.
If not, go back and read my first post, let us know if you get stuck.