Paris first or last in late April early May?

I just did a quick search and it leans towards the end of April for Paris. Cherry blossoms are mid to end of April with typically only a week of longevity. Of course, the weather leading up to that window will have an effect. I live in leaf-peeping country and we never quite know for the same reason -- the weather. It will be wonderful no matter what you decide! Bon Voyage!

lcmulvs,
We were in Giverny at the end of April in 2017 and the gardens were abloom with so many tulips! Late April or early May should be good either in the countryside or in Paris. My choice would be to spend the first night in Paris (for jet lag), then the next day head to Chartres (an overnight). The folllowing day go to Giverny early, spend the morning there (three hours is good), have lunch at the cafe there, or perhaps bring a picnic with you from Chartres, then head to Normandy that same day, staying in Bayeux for three nights. Or you could stop in Rouen overnight. That gives you two full days for the DDay sights and the town of Bayeux. (I am not one of those who wants to see every sight re DDay...one full day is enough for me.) You could then go to Brittany (it is not too far to drive in a morning) and spend the night in one of the northern towns there. That takes care of 6 (or 7 with Rouen). nights so far. Head to the Loire for the next two nights, giving you one full day to see 2 (possibly 3) chateaux, depending on which ones you choose and where you are based. Eight (or nine) nights gone. You can return to Paris for nights 9(10) through 14. One of those days in Paris could be a day trip to Reims. Remember that travel betrween places takes 1/2 to 1 day. Your longest unbroken travel day would be from Brittany to the Loire.
This is just a rough suggestion based on my trip of 2017. We had a car, so we had more flexibility than you would if you had to use the train or bus. I hope your plans work out for you, whatever they come to be!

I've been to Paris a number of times in different parts of April and May. TBH I don't think a 10 day span is going to make much difference in blooming stuff. I'd probably split and give yourself a few nights at the end of your trip to position yourself for a return to CDG. If Paris and Giverny are what you are most excited about, I'd do them first.

I will say that if you have any seasonal allergies take medication with you, the blooming chestnut trees drove me nuts year before last in April.

I'd also recommend that you walk thru Jardin des Plantes - there were some gorgeous blooming pear or cherry trees there 2 years ago. Really laden with flowers.

You should finish where your flight home is -- if you are flying out of Paris then do the rest first and spend your last 5 days in Paris. Otherwise you essentially waste the day before your flight rushing back to Paris -- and that is prime vacation relaxation time. Weather is unpredictable. Last time we were there in May it was kind of chilly and everyone was talking about how warm it had been at the end of April ---

Thanks to each of you for your words of experience! The cherry blossoms are something I wouldn't have known about, also the allergy tip and the Jardin des Plantes. And Judy, the itinerary ideas are very helpful - thanks for taking the time to think that out! I do think we'll rent a car since that seems to be what most advise when out of Paris. We've driven all over the US, but there is so much to learn about for this trip.

Normandy and Brittany can be cold, wet, and windy,, plus many of your sites to visit may be outside. I would save them for last if I were you. Paris beautiful any time of year, and there are likely more indoor activities.

That makes sense - thanks!