In general, you owe state income taxes to the state where your permanent address is located on all your world-wide income. If you work or live temporarily in another state, you also owe tax as a non-resident to that state, but only on income earned while living or working in the other state. Your home state will give you a credit for taxes you pay to the non-resident state.
Residency, or domicile, is determined by a combination of all facts and circumstances. Such as, where you live most of the time, where you own or lease a residence, where your significant family and social relationships are located, where you are registered to vote or drive, where your professional relationships are like doctor, dentist and attorney, and where you intend to return after any temporary absences. There is no specific length of time--you could change your domicile frequently, if that is your intent, or you could maintain a domicile in one state while working for months or years in another state. Here is what PA says on the matter of domicile.
https://www.revenue.pa.gov/TaxTypes/PIT/Pages/Determining-Residency.aspx
Most importantly for your situation, you can't establish a new domicile without taking active steps to abandon your prior domicile. That means things like canceling a lease, selling a home, or moving all your stuff, getting a new doctor, new car registration, and so on.
It sounds like your domicile is currently in PA and your job is in PA, so you are a PA resident. You don't need to do anything if you are planning to move.
When you move, assuming it is a change of domicile, you would cease to be a PA resident and become a SC resident. If you then also work in SC, there is nothing special about your situation except that you file as a part-year resident of both states in the year you move (you pay tax to PA for income earned while living in PA, and pay tax to SC for income earned while living in SC.)
Only if you continue to work inside PA (as a long distance commuter of some kind) after you move, or if you start working in SC before you move, then you would owe tax in two states. But nothing needs to change unless you start working in a state that is different from your domicile.