I would say 10 hours is a fair estimate for it. 5 hours is WAY too short.
Doing the lil kids mode of TJ+E2 is only about 30mins. However then the normal play through is actually fairly lengthy. Not sure how long it took me but I went through about 2 and a half podcasts so must have been around 5hours.
Fixed world play through of TJ+E will vary depending on whether you use maps or have played the game before. I think this run took me about 1 and a half hours or so.
Random world play through I would say 3 hours is a fair estimate. Depends on how lucky you get with maps and ship pieces.
For difficulty I would actually say the game could be a 1 or 2 out of 10. Simply because the games were never designed for save states and having them makes it unimaginably easy.
Also feel I should add for people that a lot of the achievements in TJ+E2 are unmissable/99.9999999999% unmissable.
The only ones I would say are missable being ''shake rattle and fall'', ''I'll just go on ahead'' and ''Cleaner, better, faster, easier''