Just got invitations to interview for Bain and Oliver Wyman (entry-level London) at mid-Jan. What do you think's the best way to use my time regarding preparation. And if anyone has interviewed with them before, I'd greatly appreciate any advices or interview experience.

going through case interview guides from vault and wetfeet would be useful. btw, you got the invitations via phone or email?

That's nice they give you time to prepare, I had a days notice for my BCG interview

Both through email.