I love Microsoft Forms records the time taken and give us a summary at the end.
Can you work out a reasonable timebox (a touch of Azure AI) based on the other submitted forms and the number of questions…. and give a little beep say every 5 minutes if they have exceeded the time that is reasonable.
One person can forget to finish their Microsoft Form and leave their browser open and it screws up all stats.
As an example everyone in my company was close enough to the 15 minute timebox – this one person ruined the stats.