Proper connection of a non-BMW provided GPS receiver to specific BMW plug

[runnerhiker]

However I have noticed it took no less than about a minute for the Zumo to also shut down following turning off bike’s ignition.

This time will vary.  I have seen a few seconds, a minute, and as long as 5 minutes.  It's still working, all is well, if you notice the variation, it's still ok.