How to use a function in setq with quote?

Suppose I'm setting a var like this:

(setq var '((:item1 "stringA") (:item2 "stringB")))

(this works)

Now I would like "stringA" be a conditional, like this:

(setq var '((:item1 (if (> 6 (string-to-number (format-time-string "%u")))
                     "stringA"
                     "stringC"))
            (:item2 "stringB") ))

This doesn't work, likely due to the quote operator (or function?). How should it be written to work?

Nothing inside a quoted list is evaluated. You have to call functions to construct the list dynamically:

(setq var 
      (list (list :item1
                  (if (> 6 (string-to-number (format-time-string "%u")))
                      "stringA" "stringC"))
            '(:item2 "stringB")))

or you can use backquote to specify the parts of the list that should be literal and evaluated.

(setq var
      `((:item1 
         ,(if 
           (> 6 (string-to-number (format-time-string "%u")))
           "stringA" "stringC"))
        (:item2 "stringB") ))

Inside a backquoted expression, comma (which looks like an upside-down quote) marks an expression that should be evaluated.