Difference on Two field values

I need to find the difference between two date & time fields , and if its difference is greater than 10 minutes, a text box should be shown ,otherwise hide textbox.

So I created a list with two fields - Incident_started - with date & time  type

                                                       Shutdown_Initiated -  same type

And created a form with two tabs .And connected date fields in form to the list

for comment section wrote a condition

 do i need to store the difference in another column in the list ? please help me in writing the condition for comment section.

Thanks in advance