It's more likely that the kind of shops which deal with articles of primary need such as food, clothes and drink (above all, drink) will open longer hours while those things such as furniture, books and electrical appliances etc. will have less opening hours.
Remember that on the 7th it is a holiday (What holiday? - San Fermin of course!) so there will be little or nothing open that day. If you need anything urgent remember that any of the peripheral towns around Pamplona will be open that day such as Atarrabia-Villava, Barañáin, Uharte-Huarte or Burlata-Burlada, which really nowadays are suburbs of Pamplona.
You might just find some small food store open in the town. But remember things like the Post Office, The Telephone Exchange etc. will all be closed.
On the outskirts of Iruñea/Pamplona there are three large hypermarkets: Eroski, Leclerc and Carrefour (Mendebaldea). They tend to be somewhat cheaper than the small shopkeeper, but it's not worthwhile unless you are going to do a big shopping. If not, the corner store is always close at hand and for sure the treatment will be more human.