Phd interview travel paid by interviewer - Is it bad form to ask to stay for the weekend? 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.
If you make it completely clear at the time of asking that you would cover all additional expenses, then staying for a day or two extra would be regarded as perfectly normal and reasonable. (Academics travelling to conferences and workshops do this sort of thing all the time.)

Indeed, it may even be regarded as a positive sign: if you do join their PhD programme, then you'll be living in the city for several years, so the fact that you want to get to know the place in advance demonstrates that you're serious about your application.

My guess is that the somewhat intimidating wording "expected ... to depart on Friday" is intended to make it clear that you can't depart before Friday.