The Portobello Film Festival is an independent international film festival based in London, which annually premiers over 700 new films, including features, shorts, documentaries, music films and animation. Additionally, workshops and talks with top film directors (such as Stephen Frears and John Maybury) are also featured. Admission to the three-week-long festival is free of charge.
The festival takes place in London within a single calendar month.
The text just says it's a three-week festival, so the festival dates could span two calendar months [e.g. December 21 - Jan 13]; this notion escaped the model.
( z1 festival :location ( z2 city :name ( z3 name :op "London" ) ) :time ( z4 within :op ( z5 month :mod ( z6 calendar ) :ARG1-of ( z7 single ) ) ) )