Three days later than what?
The form will work if you make it similar to your past tense example. You're comparing one event to another. You compared one past tense event to another past tense event.
Do the same thing with your future tense example.
I plan to be in Boston next Thursday, and I will go to New York three days later.
It doesn't work when you mean "later than now."
You can say, "Don't worry. I'll be there later." True, that means later than now.
But "I'll be there three days later" needs a future reference time.