How to add hours to an NSDate?

I have a date converted to double value and saved in database. Now, I want to compare if currentDate > myDataBaseDate + 8 hours i.e., I want to get 8 hours added to myDataBaseDate. I'm converting date into double values. So how do I get 8 hours later time from my database saved date. How do I compare

if (currentDateTime > DateFromdatabaseValue + DateByAdding8HoursInDataBase)