Valuations to IB transition (UK/EU) Advice/Guidance

Some context added below, but to keep it short and sweet:

• How long should I stay in my Valuations Advisory (Accounting/Advisory Firm) role before looking to apply to M&A Investment Banking roles?

I started my role as a Valuations Analyst at an accounting/advisory firm around 2 months ago, and I am currently studying for my CFA whilst in this role (The firm pays for this). I've seen a lot on this forum and elsewhere that staying for too long would make me overqualified for IB, yet i'm confused as a lot of people in the year or two above me who wish to make the change to IB tell me that I should complete all 3 levels of the CFA before applying (like how they are doing).

I wanted to know how common it is to switch from valuations into IB in the UK/EU and how long people typically stay in valuations before they do - and if they bother completing all three levels (or even one) of the CFA before doing so.