Complex Cron Trigger

Hi there,
Does somebody know whether it is possible to create this sort of scheduling via cron? If not, are there other ways to do it?
Wished schedule: Trigger every working day at 8pm + for the first 6 working days of a month: trigger at 7am, 11am, 4pm, 8pm.

Implementing the first part (working days at 8) is quite easy (0 0 20 ? * MON,TUE,WED,THU,FRI *), but I don’t know if its possible if cron allows the second rule with the first 6 working days combined with the first rule.

Any ideas?
Thank you