would like opinions about timing of trip to Denmark, Norway, Sweden this May; optimal time by my schedule is early to mid may for 2 weeks, was planning to head from Copenhagen to Bergen and fjords area May 7-9, see that some hotels don't open until mid may, is early May too early?

Too early for what? It's not like the countries are closed to visitors.

Weather wise you never know... was in Sweden and Denmark last May. Sweden was dreary and cold (30s or 40s F) even though a friend told me it had been sunny and warm just the week before. Denmark was dreary and cold the day we arrived but was warm and sunny for the rest of the week (50s or 60s F). Don't know about Norway... may be too early for some ferry tours and perhaps hotels in smaller towns but there should be no problems for hotels in Oslo or Bergen.

You could get the ferry from Hirtsals to Bergen via Stavanger with Fjordline https://www.fjordline.com/en/ .

Hotels in Bergen are open all year.

Weather can never be guaranteed in any country in Northern Europe. Bergen is probably the wettest place in Norway, it certainly has a reputation for rain!