The publication date is shown on the magazine's Contents page as the fourth Thursday of the month.
As a subscriber who receives his copy by post, I usually receive it the day before. I once queried non-arrival by the Monday following the fourth Thursday. I was told at the telephone that publication was not due until the following fifth Thursday.
When I pointed out that this was a week later than advertised I was told it was published on the fourth Thursday of the month unless there were five in that particular month. When I suggested to the subscription department that this meant it was published on the last Thursday of the month they seemed a bit confused!