Should cymbalta (90/day) and nucynta (tapentadol) er (300/day) be taken together?

They are both long: Acting enough that the timing is likely irrelevant. www.drugs.com has the following warning on any combination of sedating meds.Monitor: central nervous system- and/or respiratory-depressant effects may be additively or synergistically increased in patients taking multiple drugs that cause these effects, especially in elderly or debilitated patients. Best to discuss with your own physician who knows the details of your physical condition. Best wishes.

Potential problems: Those are fairly high doses of each. There is a risk of excess sedation, but also a more serious potential risk of serotonin syndrome. This is the sort of question that should really be discussed with your prescriber!