The more I've looked into the schedule the more I think it could be 29th.
In the past (even on internal selections) they announce during week (mon-fri), and they alway announce in the week before the delegation meeting. But looking at the schedule there is not an appropriate slot for the announcement on BBC 1 in that last week between 2nd - 8th.
It won't be Sat 7th as there's a pretty big Six Nations match between England and Wales starting at 4.45pm, and coverage for a match like that is usually around 3 hours. That night is also the Greatest Dancer Final, so will take up a larger slice air time.
There is a daily 45 min slot between 4.30 and 5.15 during the week, but that's not primetime and we alway announce at primetime. It could be a red button announcement I suppose but BBC have been using that less and less in recent years to do announcements.
I also checked BBC 2's schedule and there is not appropriate slot there either.