Try the attached script component. It has two functions (DoesIntervalOverlap and MergeIntervals) that it implements on the list of intervals. It would be pretty easy to mimic theses functions directly in GH, but I'm not sure about recreating how it works on the list. Regardless, the scripting component should take care of it for you.
Note: this was done with 0.7.30... let me know if you're still working on 6.xx