Here are PA's rules on establishing domicile:
To establish a new domicile, a taxpayer must:
1. Show evidence of definite intention to discontinue making the former domicile the primary base of operations;
2. Show evidence of definite intention to make the new domicile the primary base of operations; and
3. Show evidence of physical presence and abode (transient, temporary or permanent) in the new location.
If all three requirements are met, the date of the change is the first day of physical presence in the new location.
https://www.revenue.pa.gov/FormsandPublications/FormsforIndividuals/PIT/Documents/rev-611.pdf
Personally, if your New York home was up for sale on January 15, I would use January 15 as your initial date of PA residency. If your NY house was on the market, I think you satisfy all three requirements.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
