No automatic update or shared completion date should be assumed. Obtain the applicable instructions and individual assessment for the changed circumstances. Treat the wedding date and the case's dates as two calendars that touch rather than one. A marriage changes a fact from the day it takes effect; what the process does with that fact depends on where the case has reached and on the instructions given for that stage.
Record the change without promising its outcome
The FAQ recommends initial inclusion of intended eligible joining relatives; do not rewrite that guidance as either a blanket promise or a permanent bar to later changes. Actual eligibility and remaining processing still matter. Ask, before a date is set, what reporting a change of marital status requires and how quickly.
Compare that against the case's own next step, since a change arriving between two stages is handled differently from one arriving after a determination. Neither this page nor a summary of the published terms can promise how a particular change will be treated, and a hedge in the guidance is not an oversight to be read past. Where a household needs certainty for a lease or a resignation, take that certainty from documents already issued rather than from an expected sequence, and keep the resignation letter behind the document rather than ahead of it.