Even though answers here are pretty good, I would still like to share my point of view on this great question.
They didn't expect giant waves smashing whole surface.
As Cooper says on Miller's planet after being smashed by giant wave
We are not ready for this
Why did they decide to land on Miller's planet?
Miller was still broadcasting at the time - at least they thought so. They just wanted to land on the ground, pick up Miller's data (together with Miller her-self) and get back to the Endurance - this trip would take few minutes (half hour at worst) ~ 3.5 years on Earth - and then get back to Endurance ASAP with all the data they need to deeply investigate. Then, according to that research choose whether they have to travel to Dr. Manns and/or Edmunds planets, or if the data was good enough, estabilish base on Miller's planet and eventually some of them (at least Cooper) get back to home - Earth.
Important thing to keep in mind - their main goal was to save human race, not people on Earth. Most important to nderstand why did they do so, is what Doyle have said
Dr Mann's data is promising, but it's gonna take us months to get
there, and Edmund's is even further. Miller hasn't sent much, but what
she has sent is very promising. It's water, it's organics... And think
about the resources including time that would be spent trying to get
A little bit of explanation, even though its self-explaining enough - At the time, it was "the best" (in terms of being able to live there and also similiar to the Earth) planet out of these three, and traveling to Dr. Manns planet (Edmund was not broadcasting already) and back would take too much resources, while picking up data from Miller's planet would take "just" few months/years at worst (if there were no giant waves, they didn't know about) and they would still have enough fuel/resources to travel to Dr. Mann's and Edmund's planets.
As you have mentioned
However, all this time (12 years in earth time) are the equivalent in
that planet to less than 2 hours which is by far not enough time to
perform the necessary tasks to decide whether that planet is good or
not to host life.
there were some speculative things about Miller's planet in Interstellar
1) If we know waves keep coming in cca. 1 hour intervals, she sent the data almost few minutes (hour at worst) after landing - which none scientist would probably do.
2) They would have to be blind to not seeing the giant wave while landing and/or getting out of ranger - maybe even from the space.
3) How did they know there is so low water level allowing them the landing, while they didn't know there are so huge waves.