From an American:
"Finishing the week" is fine.
I think we would be more apt to say "time" instead of "moment," if you mean you went to the movies as a celebration of the week's end? We use "moment" for shorter pieces of time, usually, for example, a few seconds or minutes, "in that moment I realized how much I loved her" or "in that moment I was overcome with fear."
The use of "ad" is fine, although I think we might be more apt to say "trailer," for example, if you are referring to the short video that advertises the movie. But if you are referring to posters or other print, then "ad" is appropriate.
But I don't understand the context for "If you see an ad for a blockbuster?" Do you mean it's a great time to celebrate the week's end with a blockbuster movie, if one is available?