Your status should change the day after the TPs post which take you over the threshold.

In terms of free seat selection that should hopefully work once your account shows you as silver. Failing that, sometimes your BAEC number needs to be removed and re-entered so it re-checks your status level. You can use the AY site and AY MMB to do this, basically remove it and save, wait 10 minutes, then re-enter and save.

There is some more information in the guide here https://www.flyertalk.com/forum/brit...iers-baec.html