For the monthly updates, there is a fixed schedule which makes the update available on the 27th of every month.
You can still access and publish old monthly updates; however, they will not be shown in the new update popup anymore.
On the 15th of every month, a monthly update becomes “overdue”. That means you didn’t manage to write an update in time and should try to do that by the end of the month.
There is no real consequence if you miss an update; however, your stakeholders will see that you missed an update and might inquire why you haven’t updated them yet.