How to have a graph/chart represent whether or not a cell h as been filled

[Cities]

Hi everyone,

I am making a spreadsheet that will be used to track employee time usage. I would like to be able to create a graph of the time throughout the day that shows only whether or not the employee has entered an activity during each particular time slot.

EX: The graph shows the time from 8-10am in 30 minute increments. The employee has entered activities for the time slots from 8-9 and 9:30-10. When the graph is created, I would like to see times 8-9 and 9:30-10 filled (or, charted, or, however I should phrase it) and time 9-9:30 left blank (to represent that no work was done).

I have attached the sheet that I am currently working with. Any help would be greatly appreciated, even if it's just pointing me in the direction of some tutorials!