Didn't the Little Ant and Dec portion of Saturday Night Takeaway (whenever it appears) go out pre-recorded because of something to do with kids not being allowed in the studio after a certain time?
Not aware of it being applied on SNT in that regard apart from the obvious Little Ant & Dec recorded inserts back in the days of the original Little Ant & Dec idea and idea behind it. Anyway SNT's off the air by 8:30 most sessions so it doesn't really apply. These days though the current Little Ant & Dec appear more as stragglers, cosmetic dressings, asides and odd-job-men. That being said It seems as if since they dropped the original Little Ant & Dec interview idea they don't quite know what to do with the characters.
You may also be thinking of BGT, or more specifically BGMT where Stephen Mulhurn does a quick interview with a child act after coming off the stage and if they go onto win that night that interview gets played out as part of BGMT - it's always been signposted that these were "recorded earlier" if it wasn't already obvious from the location and the background noise as the cut-off was 10pm and BGMT goes out after that.