"I would talk to them for two hours and nothing else."
Translation:Eu conversaria com elas por duas horas e nada mais.
I fear that Duolingo tried to write it to mean the first option but it actually means the second one. I say that because, just like in English, there are better ways to word it to clarify the meaning, such as por duas horas e não mais (two hours and no more) or por duas horas e só (two hours and that's it) C:
I thought, all at once, "That's a weird sentence," "It implies something other than 'two hours and no longer' (e.g. 'talk for two hours AND something else') but I don't know what)," or possibly "I would talk to them for two hours and that's all I'd do." But if "mais" means "more," then I think they want it to mean "no longer" (or "no more" or "that's all").