Sort by start time first; it's easier to pick which event to go to if you can see all the clashing events right next to each other.
Jinja2 filter for sorting by day, where day can be None.
Utility methods on Event model, and method to transform a list of events into a grouped set.
Extract out the table view to a view helper, and show the user their favourite events (ie. their talk schedule) on their home page.