Day of the week ACL

i has been defined an ACL to permit only access to working days monday-friday
something like…

http-request set-var(req.day_week) date,ltime(%u)

acl http_working_days var(req.day_week) eq 01 || 02 || 03 || 04 || 05 
use_backend server-001 if http_working_days

but no success…
also readed this thread ACL using current system date or time?