Beth when you hesitate because Nemea may close at 3, we don't get it, unless you tell us when you will be starting from ?? ATH airport??? Delphi? 10 AM? 2pm? when u want helpful advice, please give us the prelim data. We're experienced but we don't claim to be mind-readers, LOL. If u leave Athens area by 2, plenty of time for Ancient Nemea Stadium. As for vineyards, I'll leave the research to you: http://www.ecotourism-greece.com/tourism/activity/wine_tours_greece/korinthia-peloponnese and http://www.decanter.com/wine-travel/europe/peloponnese-travel-guide-17683/2/
As for Mycenae, better in late afternoon than mid-day, tour busses will be gone. And as for time spent there.. I am a major history buff, shelves of books, several grad courses in Bronze era ... but I can do Mycenae in 90 minutes. Do some homework, have a good map along & flashlights to go down the cistern steps u will be fine.
If u decide to make a day-long "ruin-a-thon" from Nafplio, my record is this: 8 AM off for MYCENAE (do museum first, beat the crowds, then the ruins, then the "treasury" tomb), then back on road toward Nafplio ... optional 20 minute stop at TIRYNS, right by the road -- good place to eat a picnic. By 11-12 am, head EAST across the "thumb" to Ancient Epidaurus... halfway there, on Left side of road, great photo op is ARKADIKO, The Oldest known Bridge in the WORLD still in use, from BRonze Age -- https://en.wikipedia.org/wiki/Arkadiko_Bridge. At EPIDAURUS, give ruins a quickie look (not very well signaged), skip the museum (most of best stuff is in Athens museum), spend your time at the AWESOME Theatre. Read up, beforehand. Late in Afternoon, enroute back to Nafplio, use map & keep eyes on Road for ASINE ... another ruin, but the point here is beach(es). Behind ruin, an unknown sandy beach (no facilities), in front of ruin, darling pebbly beach (bring water shoes), ONE cute taverna w. sunchairs, NO crowd. Swim, sunbathe, and have dinner ... end to perfect day! I"ve done this twice. Optional ending, skip ASINE and either go up back road to PALAMIDI (closes at 7), then and/or go to ARVINITIA (Nafplio's Town beach) for a dip before dinner.