Is it possible to set up Amazon EC2 auto-scaling for particular days of the week?

I need to have a different auto-scaling policy for weekdays vs weekend.

So far I figured out how to set up the same policy for every day. The cmd call and the CRON string look like that:

as-put-scheduled-update-group-action  TNUPWN --auto-scaling-group  TNASG --region us-west-2 --recurrence "30 18 * * *" --desired-capacity 1

But when I try to set a CRON string for week days only e.g.

30 7 ? * MON-FRI * 
or 
0 30 7 ? * MON-FRI *

I am getting the error

as-put-scheduled-update-group-action:  Malformed input-Given recurrence string:30 1 ? * MON-FRI * is
 invalid
Usage:
as-put-scheduled-update-group-action
        ScheduledActionName  --auto-scaling-group  value [--desired-capacity
       value ] [--end-time  value ] [--max-size  value ] [--min-size  value ]
       [--recurrence  value ] [--start-time  value ] [--time  value ]
        [General Options]

Any ideas? Is it even possible with AWS?