A little more information on what i am trying to do.

The cells in the F column is the hours of the day, and H is the bloodpressure at the different times a day. i am trying to get the average of the hours of the night therefore it needs to be >21 and <6, as this is what the hours of the night in the project is set as.

DonkeyOte has a good point, but the question is now, how do i do it then?