Count Number Of Blank Cells In Range Starting And Ending Will Cells That Match String Values

I'm trying to develop a new daily timesheet for my production workers, where non-production items are recorded in 15 minute intervals. The user would put in "Clock in" by the corresponding time, and the same for "Clock out" at the end of the day. Any non-production items will be type in next to their appropriate time. Since clock in and clock out times will vary, I need to set up a formula that searches the array of cells for the day, finds the "Clock in" and "Clock out" values, and counts any blank cells in between them. Basically the blank cells will equal production time, and the result of the Count function will be multiplied by 0.25 to get the hours.

I am having a very difficult time finding a way to set the "Clock in" and "Clock out" cells as the range for the Count function, because it won't always be the same cells. What would be the best way to automatically have excel find the cells containing these values and set them as the range criteria for a Count function?

The formula at the bottom was one of my initial attempts, but it didn't work. I took out the '=' for the screenshot, so that wasn't the problem.