Question: I have an ISP that provides 5000 GB for use between 1am and 7am. Is it possible to schedule Geth to sync only during that time?

Answer: 
If you have a firewall that you can run that is time-based, you can simply block network connections for `geth` outside of that window. `geth` will pick up where it left off.
Note that you have to avoid fast-syncing as it must be completed before stopping.