Mine was with a decision maker for 4 weeks. I'm still yet to receive the backpayment though and I'm 11 weeks on from requesting.
I believe UC is done by area so differs in time frames, if you're allocated a work coach I believe it's usually quicker as youre dealt with by one person. If you don't have one it's chucked onto a pile to be dealt with?
I moved areas recently and where I used to live they dealt with messages in my journal rather quickly, now not so much.