What are you doing in a spike? If you can't work out after a day the rough complexity of the task (bearing in mind you should be working on a small deliverable) there's something seriously wrong. You're not meant to be doing the work in the spike. If your research spike shows that it could be a can of worms, then the outcome of it should be another ticket for a proof-of-concept for another sprint, but with specific goals (e.g. "get a POC working that does X, Y & Z").
