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.