Logistic issues for 2 day trip from Athens to Santorini??

Hard to say without specific details.

What immediately occurs as a potential logistical problem is the departure morning. How much time will you have when you get to Athens? Will the luggage storage in Athens for sure be open? Do you know where luggage storage is in the airport relative to where you need to be?

And then beyond those things there's a risk tolerance issue. If the puddle hop from Santorini is delayed significantly, you would miss your big transatlantic flight. It's a risk I would take I think, Santorini's pretty nice. Too bad you can't get one more day in Santorini and a flight home that leaves later in the day, and later in the day.

Is it worth the effort to go to Santorini for just two days? Maybe but one concern is you are flying back to the US on the same day you are flying back from Santorini.

If there is any type of delay you could miss your flight back to the US and end up paying who knows how much more for a ticket(s)

You may want to consider a nearby island like Aegina which is quicker and much easier to get to with far less chance of delays. Aegina has everything one would want in a Greek Island and far less expensive.

You'll still need to get to the airport the same day regardless of where you go.

Why not spend the time in Athens as there is so much to experience there and have a much better chance of no problems getting to the airport?

It is very easy to fly out of Santorini. We recently completed a 3 day trip there. What we did was take an evening flight from Santorini to Athens, so we had the full day on Santorini. You only need to get to that airport 1 hour in advance, and it's a relatively small island. So we had the full day to explore Santorini, flew back to Athens at night, stayed at an airport hotel (Peri's), and flew home the next morning. If that can work for you, removes the risk mentioned.

In addition to the risks of missing your flight to the US which have been exposed in the previous messages, to take a Santorini → Athens flight on Tuesday morning with Aegean you have 2 possibilities: The 6:05 a.m. flight or the 8:30 a.m. flight.

Only the 6:05 a.m. flight arrives early enough to connect with your transatlantic flight with a safety margin.
In return, he will force you to get up at 3.30 a.m. at the latest.

In fact, as soon as you arrive in Santorini, you will have to think about organizing your hotel checkout and your hotel → airport transfer in the middle of the night.

You would probably spend two more pleasant days staying in Athens

I think this risky idea stems from the familiar FOMO (Fear of Missing Out), triggered by (1) "Oh you MUST see Santorini" from friends who spent 4 hours there once, on a cruise... or (2) too much time on YouTube. Yes, the Famous View can be worth in on another visit ... perhaps schedule a future 2-week trip to enjoy several Greek islands, since the RS trip covers none.

Adding having to retrieve bags from some sort of storage area eats up the precious little time you have.

Taking the 1055PM flight Monday gives you the same number of daylight hours in Santorini as taking the 6AM flight Tues., and eliminates a lot a risk and lets you get a good nights sleep.

Do you have a single ticket booked from JTR-IAD or are you doing a DIY 2 ticket adventure?

I see UAL does sell the JTR-IAD with the 830AM JTR departure and connecting to the 1145 ATH departure.
If that is the single ticket you have I would take my luggage with me so I could check it through when departing Santorini and not have to take the time to go retrieve it and make another trip through security.

Taking the 1055PM flight Monday gives you the same number of daylight
hours in Santorini as taking the 6AM flight Tues., and eliminates a
lot a risk and lets you get a good nights sleep.

Great idea Edmonds Joe. Short flight + staying right at the airport in Athens = several more hours of sleep. Particularly nice given that getting some decent sleep before you then deal with jet lag on arrival home is key to adjusting to the new time zone.