I have been shortlisted in the Phd application process at a research institution in a neighboring European Country. I have therefore been invited to go there for a serie of interviews, visits to their laboratories and informal meetings. All of this will last from Tuesday to Friday and the institution is paying for all travel/hotel expenses.
Since I have never visited that city, and the interviews take the whole week, I would enjoy spending the weekend there and flying later on sunday.
In the forms they provided they write explicitly
Please note that you are expected to arrive on Tuesday and depart on Friday
Would it be bad form, or put me in a bad light, if I politely asked to delay the return flight to sunday? Of course I would take care of my accommodation expenses for the extra days.