Add/Subtract Time over a new day?

I have a spreadsheet where I am tracking time spent on sleep (11 week old baby, yay!), but some of the sleep sessions roll into a new day. For example, one goes from 9:00pm on January 10th to 3:25am on January 11th. Through the day it's no problem to track the hours spent sleeping but I get an error when the formula crosses a date line. Can anyone help me?

Hi Jeff - They are in separate cells. I'd like to keep them in separate cells if possible - I'm looking at patterns across dates, days of the week, and times of day, so it's helpful to have all of those in separate fields. Thank you so much for your help!

Are you able to use PowerQuery?

Ha!! Thank you! I'm not really fretting over it too much - more than anything I'm just enjoying my little tracking project She's been having some nap issues for the last few weeks - wakes up after 40 minutes with alarming consistency, though not for every nap - the consistency is the 40-minute mark, not which nap she wakes up for. So I'm doing some investigating, and I have found that almost every 3:15-ish nap is a bad nap. So, why? The sun sets on that side of the house, so maybe it's not dark enough in her room - but no, I darkened the room with a sheet for three straight days, and nothing changed. So, on to the next possibility! I'm pretty sure the answer is that she's an infant. :D She has slept through the night a couple of times though, so I'm also looking for correlation between those days and nights - were they both Fridays? Were they both followed by days with 6+ hours of awake time? lol. By the time you figure one thing out, everything changes anyway. But we are having the time of our lives!