Excel graph question (number & date)

Hi all,

I feel quite silly for not being able to figure this out. We queried some data using a plugin in Excel, to display resource consumption in our factories. In this example we're looking at the water consumption as measured by sensors across a 20 minute period: 

The consumption total column is formatted as "number, 9 decimals" and the Timestamp column has been formatted as "Time, hh:mm:ss" but tried custom as well. 

Over this period I'd like to make a super simple Excel graph, a line going up showing you when we used what amounts of water. However, the timestamp gets converted into a number which results in this:

How can I best display the consumption of water without seeing the timestamp as a line? I want the timestamps simply on the horizontal axis. Sorry for asking something so basic!