5yrs ago I was roughly the same, depends how much you commit up front. I had minimal FP experience, so I bought "Domain Modeling Made Functional" [1] by Scott Wlaschin and used it for side projects / class libs first. Took about 6 months to experience the full mental shift.
Even if you eventually decide you can't commit a team to F#, it's highly worth it because doing at least one app in F# will vastly improve your C# and how you structure applications. [2] I personally just got addicted to the expressive power, it's hard to replicate with any other ecosystem given the full power of .NET under the hood. Giraffe is also a great place to start if you know ASP.NET Core. [3]
I didn't have c# exp and it took me a month to feel "productive comfort", and less than 2 months until i felt "native comfort". I've been using it for about 2 years now.
That said I:
• had zero C# experience and it was the C# interop that caused me the most pain. Its easy now but I didn't grok how to properly pass arguments to overloaded C# methods (i kept messing up parenthesis, commas, and didn't pass argument names to tell f# the right function signature)
• have been coding for 8 years
• have functional lang experience with elixir and elm.
