The timing: the window a notice has to beat

A window is measured from the moment a notice arrives, not from the moment it is written. Sample I sets four windows against five channels and finds that the choice of channel, not the length of the window, decides whether two of the four are any use at all.

Desk spec

windows: 4
longest: 30 days
shortest: 2 days
survive the post: 2 of 4

the five kindsA receipt records something that already happened, marketing promotes something, a service note explains a state of the account, a security alert says something changed, and a legal notice is the message whose arrival is itself a step.

the two switchesOne stops marketing and nothing else - 12 of 50 messages on the samples. The other does not stop anything: it changes the channel the remaining 38 travel on, which changes how they arrive and what they prove.

the three countsSent is what the operator's log holds (50 of 50), arrived is what a delivery receipt shows (48 of 50), and read is what a read receipt shows (21 of 50). Three counts, routinely called one.

Direct answer

Four windows are common: thirty days for a change to the terms, fourteen for a closure, seven for a bonus expiry, and two for a limit change. Arrival time is subtracted from each, so posting a two-day window consumes it before it starts. On the samples two of the four windows survive a postal notice.

Four windows, one subtraction

The usable window is the nominal window minus the time the chosen channel takes. For an electronic channel that subtraction is invisible; for post it is not.

Sample I - four windows against the arrival time of two channels
Window	Nominal	After email (0.9 s)	After post (2 d 6 h)	Survives the post
a change to the terms	30 d	30.00 d	27.75 d	yes
a closure of the account	14 d	14.00 d	11.75 d	yes
the expiry of a bonus	7 d	7.00 d	4.75 d	partly
a change to a limit	2 d	2.00 d	-0.25 d	no
four windows	53 d	53.00 d	44.00 d	2 of 4 survive

sample I - the subtraction, shown nominal windows 30 + 14 + 7 + 2 = 53 days email drag 0.9 s = 0.0000104 days, so 53.00 days remain post drag 2 d 6 h = 2.25 days, so 53 - 9 = 44.00 days the two-day window posted on the day the decision is made arrives 0.25 days after the change it announces 30 - 2.25 = 27.75, 14 - 2.25 = 11.75, 7 - 2.25 = 4.75, 2 - 2.25 = -0.25 so the arithmetic decides it: the same decision, announced on a different channel, has a window or does not.

The channel chooses the window

That result is the reason the channel grid and this page belong next to each other. A reader who has moved notices to a paper or a truncated channel has not merely changed how the message looks.

sample I and C - the same notice on three channels email arrival 0.9 s -> window intact push arrival 1.2 s -> window intact, but no durable copy SMS arrival 3.4 s -> window intact, text truncated post arrival 2.25 d -> window reduced, and gone below 2.25 days 3 of 4 channels keep the window; 1 consumes it the notices whose windows are shortest are the ones most often moved to the slowest channel, because they feel less urgent.

How to use a window

Windows only help if the reader knows which one is running, and the count starts in a different place for each kind.

Find the window the message names, then subtract the arrival time of the channel it used.
Treat a two-day window on a paper channel as already expired, and say so while asking for the date.
Note which channel your notices use now, because the grid permits only some of them.
Count from arrival, not from the date printed on the message.
Ask for the effective date in writing if the window depends on it, and keep the reply with the notice.

The timing: the window a notice has to beat

Four windows, one subtraction

The channel chooses the window

How to use a window

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