Time/Date Graph

Ok guys, unfortunately I have fallen rough in my memory on how to really graph things anymore. Attached in the excel in question. Here is the description of what each column is:

A: Start Date - this is the date the test was initially executed
B: SLA - This is when the test need to finish by
C: This is taking the SLA and adding the Aging time to it (Currently this is manually being done, I can't get the formula to actually line it up correctly because of the timing explained further down)
D: Aging - This is when the test completed (This is tricky because it's in military time for example 4:33 means 4:33 AM the day after the test started, therefore 23:46:00 means it actually finished before midnight the day it was started)
E: Variance - I was attempting to show the time it took compared to the SLA, obviously I'm running into an issue with the variance as you cannot have a negative time, so something that finished before midnight, it showing the same as something that finished after the SLA deadline.

The objective is to be able to track changes that are being done to the data of the test, in theory, the SLA will always be 7 AM the following morning, but the goal is to have the test finish as soon as possible. The further down the data you get, the better our timing is getting as it actually finished before midnight once. I'm trying to come up with the best way to graphically represent this data. I thought a line graph showing the data point would be the best, with the middle line being the SLA (7:00 AM). I am open to suggestions if there is a better way to set up the data or configure the graph.

Objectives: Automate Column C and provide a graphical representation of the data.

Thank you in advance!

-Sean