How to compare time and find the delay time?

Question

hi ., i need (logintime in one table and fixed working hours is eg:9 but a employee login at 10 o clock the delay hours is 1 hour . fixed working hours is saved in one table as companytime(tablename) and employee login time is saved in another table as logintime (table) i need  to compare both the table and need the delay time )

Eg: Logintime is 10
    fixed time is 9
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delay is  1 hour 
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using asp.net using c#