Line Chart - Problems with labeling X-Axis

I am trying to create a line chart but am having trouble with labeling the
X-Axis. The graph is charting temperature on the y-Axis and the date and
time of the testing is running along the X-Axis. There are at least 1096
time entries and I would like the X-axis labels to only display the date
which is only two days and not the time (reason for all the entries). The
X-Axis is currently displaying the time at a 90 degree angle and only one
date at an 180 degree angle, becuase of the numerous time entries the second
date does not show up along the X-Axis. Please help.