Hi Jon, welcome to the Gibbon community 
I’d be happy to work with you and discuss any changes you’re aiming to implement, as the (newly minted) Gibbon Maintainer. We have a Slack channel for developers, if you send your email address to support@gibbonedu.org we’ll send an invite.
One approach to tackling the timetable issue might be to use the built-in Google calendar integration. It’d only work if you’re able to use the Google login option, however if you do then the timetable can overlay any calendar events from both a school-wide calendar (for regular classes) and a teacher’s personal calendar (for private lessons). Google’s calendar has decent tools for setting up ad-hoc and recurring events of all sorts, so this option may be worth considering, and may get you up and running with less initial development time.