Time limit for reporting a change

Please can you help.
We have a scenario where a client has won their DLA appeal for a dependant and had this backdated to the date of claim.
In law, how long does the client have to report this to the DWP to have the Disabled child Element and Carer element added to their UC with a backdate to date of award? Do they need to inform UC within 1 month of receiving the decision from HMCTS or within the assessment period that the Tribunal DN is issued?
Thanks

I dont think you need to worry

Paragraph 21 of Sch 1 Universal Credit etc (Decisions and Appeals) regs 2013 provides

“21.Except in a case to which paragraph 22 or 31 applies, where the superseding decision is advantageous to the claimant and the change of circumstances was notified to an appropriate office after the end of the assessment period in which the change occurred or after the expiry of such longer period as may be allowed under regulation 36 (effective dates for superseding decisions wherechanges notified late), the superseding decision takes effect from the first day of the assessment period in which the notification was given”

Paragraph 31 in so far as is relevant provides

“31.—(1) This paragraph applies in relation to an award of personal independence payment or universal credit where the change of circumstances is that the claimant or, in the case of universal credit, a member of their family, becomes entitled to another relevant benefit or Scottish disability payment, ceases so to be entitled or the rate of another such benefit or Scottish disability payment alters.
(2) Where this paragraph applies, the superseding decision takes effect from—
(a) where the superseding decision concerns universal credit, the first day of the assessment period in which—
(i) the entitlement to the other benefit or Scottish disability payment arises;”