How quickly can I renew my passport through US Embassy London?

I currently have a passport renewal appointment for 21 November. I need to travel on 28 November. Can I get my passport renewal done that quickly? Does anyone know how much extra it costs?

I was going to cancel the appointment and book for when I come back, but then realized that maybe I can just get it renewed in time?

https://uk.usembassy.gov/u-s-citizen-services/u-s-passports/how-to-renew-a-passport/processing-times/
Normal processing through the US Embassy in London (via post or appointment) is somewhere around 3 weeks. If you can go this route after you return from travel (and aren't going anywhere that requires 3 or 6 months validity left on the passport), then it would be simpler.

But from what I could gather recently from the website, it's possible with an in-person appointment but most likely it would be a limited validity passport. I don't think it costs any extra, however after your trip you'll have to apply by mail to exchange your limited validity passport for a full validity passport. If you go that route, make sure to bring proof of your travel plans to the appointment.

We renewed ours this July through the US embassy in London and it involved their preferred carrier service collecting our applications, delivering them and returning the new passports. From the day the applications were delivered to the Embassy to the day we received the new passports was just over 2 weeks.