Meta is frozen but if they are actually hiring for the role and dont just have the req open for show, it can take five to ten weeks on average. Considering the latest earnings call, I'd say maybe 6-12 given the holidays are here in the US and I doubt any UK offices would be operating independently right now: Usually it's Resume screen-> Recruiter phone screen -> TPM phone screen: one or two interviews-> TPM onsite: typically five interviews

For topics, have all your stories related to technical projects, architecture and system design, partnerships, collaboration and leadership ready to go. Topics about risk may also come up so have a couple of examples technical risks and tradeoffs you had to consider.