It's 10 calendar days. Under the PA rules of civil procedure, you don't count the first day but you do count the last day in determining the 10 days. In addition, if the last day under that computation falls on a Saturday, Sunday, or a state or federal holiday, that day is not counted and the next day that is not a Saturday, Sunday, or legal holiday is then the last day for filing.
Whenever you see something is due in X days, always assume it's calendar days unless the document says otherwise or you verify the rule. That way, you are always safe. If you assume business days and turn out to be wrong, that's a real problem. If you assume calendar days but it turns out that it was business days, then you're no worse off except for the pressure of getting it done a few days earlier than required.