matplotlib: show xticks only for discrete times

[speedy66]

I am plotting data that depends on time and height using pcolor. The data is
collected every 30 minutes, so there will be data at 1PM and again at 1:30PM
for instance.

My question deals with how to get xticks to show up only for time values
that actually exist in the dataset. As an example, ticks will currently
appear at a time that corresponds to 1:24PM which is not a time where data
exists. These values change as I zoom in also. I'm using
matplotlib.pyplot.

I've tried searching around for the answer, but have not been successful.

Thanks in advance.