In our current system, a game assigned as a Homework can have a maximum deadline of 14 days(2 weeks). However, we are working on increasing this time frame as it is requested by many.
For now if you wish to have a deadline for more than 14 days, you can extend the deadline of the quiz for the required period a day before the deadline expires.
This short clip demonstrates how to edit the deadline:
We understand that this is not an ideal solution but this can be used as a workaround for now.