To be safe, yes - however, they often word the question as "with close reference", so I don't know how true this is, but my teachers said that technically you can treat it as a stimulus and make it part of your thesis instead. How true is this? No idea!
Honestly though, I'd just analyse it on the spot, haha...just more short answer practice!
edit: I just checked the marking criteria for the 2021 Mod B question, and it says:
- Explains skilfully the ways the excerpt/screenshots reflect the concerns and aesthetic qualities of the text
So I guess you do have to analyse it to some extent. Honestly though, excerpt questions are really confusing, because in that case why can't your whole essay be on that extract? So actually it probably would be most effective integrated into one's thesis, but also analysed in the relevant section.