Universal Credit Work Capability Assessment delay

Hello, apologies if this has been brought up before - can’t find anything that specifically relates however.

I have a client who completed a UC50 and DWP confirmed receipt of this some 9 months ago. He’s asked on his journal when he’s likely to be assessed and has been advised that the DWP have up to 24 months before they are obliged to assess. Not uncommon for these to take many months to come about, but does anybody know if the 24 month quote is written in policy anywhere?

Callum