Currently, Hayfever only lets you manage timesheets for the current day. Plan to include support for selecting a different day and managing its timesheets.
Timers should only be allowed to be started for the current day, but previous days' timers can be stopped.
Evaluate whether WebSQL would be more flexible for managing days and timers independently, ditto for projects & tasks.
Look at Lawnchair.js and see if it's a decent compromise between localStorage and WebSQL.
Currently, Hayfever only lets you manage timesheets for the current day. Plan to include support for selecting a different day and managing its timesheets.