10 days in Europe

Early May can still be a little chilly in Greece from my research. Where in Greece were you planning?
I'd also consider southern Spain and perhaps Sicily.

Do you mean Greece, Greece as in Athens or the islands. You will not find beech weather at that time as everything only starting to warm up. Warm would suggest southern Spain, Italy, Portugal. Anything through central France, Germany, could be chilly and rainy. The weather at that time of year is very difficult to predict because it could also be warm and pleasant. It is a dice roll but I would prefer to be further south.

I am not a beach person. I was planning for Athens, Rhodes, and Santorini. I was thinking more of just having good weather to hike and see the areas. I am not wanting to go to Italy right now, I was there last year and in September spent a couple days in Venice.

The warm is more just looking for spring weather. 70ish and not terribly rainy.

So you are flying out of England on which date ? The 29th ? So you need to back in England on May 7 th ?

So you have from the 30 th till the 7th really .

Mallorca is lovely , Palma de Mallorca is so beautiful ( and the old town is so " quaint " ) , you could do three days there then four in a smaller town .

If you still want to go to Greece ( and I don't blame you I LOVE the islands , we actually did just 8 days there this September) I would see where I could fly into direct from London on my dates ( it's NOT as easy as you think as it's not high season yet ) , likely mykonos and or santorini ( and I say this even though I prefer Naxos over Mykonos but you'd have to take ferry and they only run on a much reduced schedule off season and depending on when your main flights arrive and depart it can make things complicated )

I did look at the flights. There is a non-stop to Athens, actually several. Then my last day in Greece will be in Santorini and luckily there are direct flight from there to London.

Check your potential destinations on a weather website. Wunderground has day-by-day stats so you are not dependent on just averages. I see on Wikipedia that the average highs in Athens are 68F in April and 77.4F in May, so I would not be confident of weather above 70F at the beginning of May, assuming you care about something other than mid-day temperatures. I know how easy it is to look at monthly averages and somehow assume they are minimums. Not even close.

I've linked to the Athens data for May 2016, which was cooler than this year. As you can see, there were some lows below 55F--certainly not cold. Unfortunately, there's a lot of missing data from Athens, so you won't have the usual 20 year's worth of statistics to look at.

If you place a premium on warmth, you might do better in a place like Seville, but you could still encounter lows in the lower 50sF.

I've never understood what an average monthly temperature means, except that overall one month may be warmer or colder than another. Is it an average of the daily highs and lows? or the average of the hourly temps? Even an average HIGH temp for a month would tell more. Which is why I go to one of the websites that has daily historical data for several years back and look at the range of dates around my proposed visit.

I can tell you that I was in Athens and the Peloponnese this year from April 20-May 6. I needed a like jacket in Athens for the first 2-3 days, but by May 1 was often looking for shade!

I've never understood what an average monthly temperature means,
except that overall one month may be warmer or colder than another. Is
it an average of the daily highs and lows? or the average of the
hourly temps?

It can be any of those things. Gotta read the fine print.

Ten days split between Greece and England means a short visit to both. Why not skip one?

We love Britain and Greece. If you love history, Greece has it in tons. Plan on at least two full days to see the Acropolis, other sights in Athens and New Acropolis Museum. If time see the Archaeological Museum.

There are islands near Athens that you can see from a ferry. It is a day tour. I think the islands include Aegina and Portos.

I am only going to be spending the first couple days in England. Planning on only going to Hever Castle and will be staying there. I spent a lot of my time in school studying Tudor England and when I went to London in September I didn't get a chance to get there.