Counting hours since last day off

Hi there. I'm currently working a job that allows me to take a day off when I reach a certain amount of hours worked. I'm creating a spreadsheet to help track this. Is there any formula that I could use to track the amount of hours I have worked since my last day off? For instance, I have a column that has a cell for each day showing how many hours i worked that day. When i take a day off i will fill that days cell with the word "DAY OFF", I want the function to return the total hours worked since the last "DAY OFF". Any help would be great, thanks in advance!