Any reason for you to not use the timing question type?

I have those for the first two pages of the instructions, but the time I want them to spend on page 3 depends on how long they've spent on pages 1 and 2, so it's not always going to be the same

rma703
Try this; I have made slight modifications in QID change it as per your survey. It will be a text entry value and within survey make a content validation of it to be number. Add it in questions you want it to work.
Qualtrics.SurveyEngine.addOnReady(function() {

 var qobj = this;

 qobj.disableNextButton();

 var msTimeRemain = (5*60*1000)-(Number("${q://QID13/ChoiceTextEntryValue/7}")*1000) -(Number("${q://QID15/ChoiceTextEntryValue/4}")*1000 -(Number("${q://QID14/ChoiceTextEntryValue/3}")*1000))

 // ^ Update QIDx to QID of timing question on previous page ^

 if(msTimeRemain>0) setTimeout(function() { qobj.enableNextButton(); },msTimeRemain);

 else qobj.disableNextButton();

console.log(msTimeRemain)
});

Hope this helps!

It unfortunately didn't work. Do you know if I need to update this part of the code?
"ChoiceTextEntryValue/3}" Not sure where this value comes from

rma703
Yes, you need to update that you can get that value easily. By clicking on the piped text on any question text and pipe in that value in any question or also within survey flow in front of embedded data and once entered just copy it and paste in JavaScript.
I was able to make the code work with those piped text values.
Hope this helps!