Greenbox delivery days

Greenbox delivers on Tuesdays and Fridays. A subscriber picks a delivery day
when they sign up, and that day is fixed to the subscriber's postcode rather
than chosen freely: the routing engine assigns each postcode to one of the two
runs so that a van covers a contiguous area in a single morning. Subscribers in
a postcode served by both runs may choose either.

A delivery day can be changed once per calendar month from the account page.
The change takes effect from the following week, not the current one, because
the packing list for the current week is frozen at 18:00 on the day before the
run. A subscriber who changes their day twice in a month sees the second change
rejected with a message explaining when the next change becomes available.

Deliveries arrive between 6am and 2pm. Subscribers receive a text message with
a two-hour window on the morning of the delivery, once the van has been loaded
and the route has been sequenced. The window is an estimate; a run that falls
behind pushes every remaining stop later, and the subscriber is sent an updated
window when the delay exceeds forty minutes.

Boxes are left in a safe place when nobody answers the door. A subscriber can
record delivery instructions on the account page, including a photograph of the
preferred spot. If no safe place has been recorded and nobody answers, the
driver takes the box back to the depot and the subscriber is charged as normal;
the box is not redelivered, because produce that has spent a day in a van is no
longer produce anyone wants to eat.

Public holidays move the run rather than cancelling it. A Tuesday holiday makes
that week's Tuesday run happen on the Monday, and a Friday holiday moves that
run to the Thursday. Subscribers are told about the shift in the weekly email
sent on the Sunday before.
