It's been 48 hours since elections started, which means that the banner goes away. However, I noticed that on Gaming Meta, the banner is still up. Checking the data says it isn't going to expire until February 15th, which is almost two weeks from now.
I can't check the dates on other sites, but I did notice that they also still have the system message on their per-site-metas.
I did a bit of experimentation. Which knocked our meta banner out of commission, but you can still see it on Web Apps and on AskUbuntu. It seems that we're still barred from setting it longer than 48 hours on those places, but the original message set by Community is allowed to stand for longer. Is this intentional?