There can be two math lessons on one day, but they need to be placed consecutivelly
If you have 6 math lessons per 5 day week, then two will be on one day. In this case you can tell the software to place these consecutivelly:
Add a new cardrelationships and select entries marked by red color:
The green color is optional, if for example you have 6 math lessons, the software will by default spread them on 5 days(one day will have two lessons).
But you can tell the software to place 6 lessons on 4 days. Or as shown on the picture you can let the software to decide if 6 maths will be on 4 days or 5 days.