Is this itinerery doable

Tas,
I have visited both Corinth and Delphi while visiting Greece, although at two different occasions.
Corinth is rather close to Athens, while Delphi is a bit longer to reach. My most recent visit to Corinth was on a land tour while in the Piraeus port of Athens on a cruise ship. The trip to Corinth took way longer to get there, due to the very heavy traffic. Our time in Corinth included a short boat ride on the Corinth canal (canal that cuts across the isthmus). I highly recommend taking the Corinth Canal boat ride. If you do that, your trip to Corinth will take up most of the day, due to heavy traffic.

The Delphi trip, I took by renting a car and I spent about 3/4 of a day including travel time. It was in March and not crowded with tourists.

I don't recommend trying to do both trips in a single day.
You are planning to do the trips on separate days. However, you might not want to drive to Corinth considering the heavy traffic. The roads were too small for all the traffic.

Consider taking a day trip to Corinth. Explore options for transportation. Look at tours. https://www.viator.com/Athens-tourism/d496-r1241348686842623-s322637681?mcid=33953&supbk=1&tsem=true&supci=-1215822010&supag=1241348686842623&supsc=kwd-77584351893120&supai=77584364642296&supdv=c&supnt=s&supkw=viator%20tours%20from%20athens&supti=kwd-77584351893120&suplp=74909&supli=45874&m=33953&supag=1241348686842623&supsc=kwd-77584351893120&supai=77584364642296&supdv=c&supnt=nt:s&suplp=74909&supli=45874&supti=kwd-77584351893120&tsem=true&supci=kwd-77584351893120&supkw=viator%20tours%20from%20athens&msclkid=f414ae10cf8f118e4511f049f531d97e

I didn't see a tour of just Corinth from Viator, but do some research, you may find one. Also, you may decide to rent a car, but suggest checking the route to see how long is the trip.
Further, not sure about accommodations in Corinth. We didn't see a modern city there.

It's doable, but not desirable. Corinth, which is not the Peloponnese, does not need a full day. Do you have in mind what you want to do with that day? We stopped in Corinth en route from there Athens airport to another destination in the Peloponnese, walked across the bridge, ate lunch, and that was sufficient. If you want to only see the canal, you will only need 2 hours to visit, then I would head to Delphi and sleep there. Spend the second half of that first day, and the first half of the second day in Delphi, and then return to Athens. Of course if you choose a boat ride as described above, then you would need that full day

I am planning to do this in 1 day
Corinth Canal, Ancient Corinth, Mycenae, Nafplio, and Epidaurus
spend night in corinth.
Then next morning drive to delphi

We spent about 2/3 of a day in Nafplio, but that included walking up the more than 800 steps from the city to the fortress above the city. I don't see how someone could do 3-4 places all in one day.

I suppose that when visit these ancient sites, I take time to absorb the details and natural scenic views. Again, we had a guided tour of Corinth that went into the detailed history of Corinth, as well as the site itself. The short boat cruise of the canal was great.

Hope the traffic is better than what it was when we visited Corinth.

Delphi is definitely a place that you want to take in the magnificent views as well as the archaeological details.

What you are proposing certainly would not be enjoyable. I don’t know about possible. Why don’t you figure out how long the route you are proposing would take to drive, add time for meals, parking ect. Then see how much time would be left in the day for each place you want to visit.

And look at times the sites are open. March would have winter hours which I think are about 3 pm.

But I wouldn’t do it. Sometimes less is more.

Thank you all for your responses. i will certainly re consider my plans.