DateTime Picker comparision

Question

For one of my project which is regarding Prison management, it says I need to release the prisoners if they have 7 days left in prison. I have my Date_of_Entry and Date_of_Release. What I want to do is, I want to subtract the Date_of_Release from  Date_of_Entry, so if it is less than 7 days it shows 'released' else "can not be released". I would be glad if anyone could help me with this. Thank u in advance :)