Here's the data I want to plot with multiple lines, one for A, B and C, which
are quantities of things. The start time actually represents the start of an
hourly window when these things accumulate. So one would read this as
"Between 7:00 and 8:00, 944 things accumulated, 786 of them were B things and
158 were C things.

Start A B C
07:00 944 786 158
08:00 24,445 21,802 2,643
09:00 61,540 56,505 5,035
10:00 62,938 57,748 5,190
11:00 59,737 54,864 4,873
12:00 42,903 39,228 3,675
13:00 48,001 43,873 4,128
14:00 53,206 48,839 4,367
15:00 49,850 45,613 4,237
16:00 30,668 28,066 2,602
17:00 8,912 7,858 1,054
18:00 2,445 2,113 332
19:00 201 168 33

I created a line chart with 3 series, the A, B and C ranges. The x-axis
labels are the start times. When plotted, with the data table displayed
below the graph, in each column of the table is:
Start Time
A value
B value
C value

which is fine but the time is just the start time of the window, not the
actual time when those values occurred. To make it somewhat more readable, I
took Jon's advice and change the start time to the duration of the window.
When that's plotted, it looks like the first quantity is collected at the
middle of the time window, like 7:30. That's obviously also not true.

Any advice on how to make this more readable?

Thanks.