Task Entity Provision in Home Assistant

The basic requirements of task entities:

Allow a task entity to be set with a due_at datetime.
The task has a lead time-frame. When the current time becomes (due_at - lead), the task state is set to "on". e.g. if the task has a 3 hour lead time, then the task becomes due 3 hours before the due date.
As the due_at approaches, show the task in a checklist.
when the task is checked, the task state is reset to "off". clear/reset the due_at and remove from the checklist.

Each task should be assigned a schedule, which defines how the due_at is updated:

an 'ongoing' schedule declares that the due_at is reset to a set amount of time in the future every time the task is complete e.g. "Drink Water" once per hour, "Open Curtains" once per day, "Vacuum Floors" once per week.
a 'custom' schedule declares that the due_at is set by external automations

Task group entities could be used to set multiple task entities as due together:

A task group has a due_at that cascades its value to eack task in the group.
The task group inherits its lead from the maximum lead of the tasks in the group.
All incomplete tasks in the group are listed in the checklist
When all tasks are complete, the group is also marked complete.

To extend this, additional information could be stored:

a history of each time a task is complete and who completed it
provide insight into the value of tasks
keep a tally of brownie points for individuals