There are a number of ways you could implement this depending on what exactly a 'turn' means in your story.
1. Does a 'turn' pass each time the Player selects a particular link related to the current Location/Room?
eg. Does the room have a Wait (like) link that increments the numeric value of your $tuns variable.
<<set $turns += 1>>
... if so then you could place the <<if>> related macros within the body of that <<link>>.
2. Does a 'turn' pass each time any links related to the current Location/Room are selected?
<<link "Room Option 1">>
... do something ...
<<link "Room Option 2">>
... do something else ...
... in this case you may want to create a custom widget to store the <<if>> related macros in and then call that custom widget within each of the bodies of the Room related links.
3. Does selecting any links in the story's interface increment the number of $turns?
... if so then you might be able to use the Config.navigation.override setting to intercept the selecting of any link and call the custom widget from point 2 from there instead.
4. Does the passing of real-world time increment the number of $turns?
... if so then you will need to attach a timer handler to monitor the passing of time and then call point 2's custom widget from it instead.
5. Some other meaning of 'turn' or some other way of incremental the number of $turns....