By default, Maple TA is configured to log out the user after 30 minutes of inactivity. Browsing through and answering questions, clicking on "Verify" etc. will reset it back to 30 minutes. 
The pop-up appears after 25 minutes of inactivity, clicking on "extend session" during the next 5 minutes will reset it back to 30 minutes as well. If the user is too late and clicks "OK" past 30 minutes mark, Maple TA will redirect to the login page. 
If one single question takes more than 30 minutes to solve on paper and causes Maple TA log out in the mean time, I would strongly suggest to split it up into multiple parts (multiple questions or multiple verify sections within one single question). Not because of the logout issue, but because it will give you a better insight on the student's ability and provide you with more flexibility on partial grading.