plot_date - extra values added that are not in my data

Hello,

I have been wrestling with matplotlib all evening (im completely new
to it since a few hours ago) and finally almost have my graph
finished.

There is just one thing left that I can't seem to figure out myself.
I have attached the graph for reference (hope attachments are
allowed).

It is a date plot, my data starts at 16:58:11 and ends at 17:25:14 but
for some reason I am being given ticks for a few minutes before and a
few minutes after.

Is there some kind of compress, or trim function that I can use to get
rid of these and have the axis start at my first data point and end at
my last. Or at least the nearest major tick?

Cheers

test2.png