Adding new Circuit to BGP For internet, first time doing it need to report possible downtime to upper management

We essentially have block IP space x.x.x.x/24. We have 3 Providers and were about to add a fourth, an ATT circuit.

I've set up BGP on our end, the link is up, I'm just waiting to "schedule" a time for ATT to do their end.

What's the possible down time here?

I personally think there won't be a noticeable down time as the route populates through ATT's back bone, or while ATT owned spaced populates to our router, but shouldn't be long, or?

And if anything does happen I should just be able to unplug the link to break BGP.

Thoughts?

Thanks