unfortunately, that's not possible right now, but we may consider adding more complex recurrence syntax in the future. You're welcome to add your vote for this request in our Votebox: http://todoist.com/Vote/showProposal/22/
For now, as a workaround, you can set up 2 tasks with the same name and schedule one of them to:
every weekday at 3:35pm
and the other one to:
every Sat, Sun at 1:00pm
During the weekdays, you can check off the first one and the second one during the weekend, but if both have the same name, it will appear on your 7 days list as if it was the same task.