As I understand season in polish is "pora roku" which is something like "a period of the year". I think okres refers mostly to a span of time in a more general sense. "Pora" also means period. Now, what is the difference between "pora" and "okres"? is a pytanie I do not have an odpowiedz for :(
Could you describe more specifically the nuances of how okres is used? I am completely unfamiliar with this word.
Also, could this be translated, "This is not a good time period"? Like, I don't like the 1800's. This is not a good time period.
I also have to agree with everyone else and say that period is not used alone like this to describe a period of time in English.
I added "time period" and even made it the best answer. That's basically what it means. Please note that "okres czasu" is something that you can hear quite often in Poland, but it is actually the most common example of a pleonasm (I personally disagree because 'okres' has other meanings and the 'time' part isn't obvious, but well, it's not up to me to decide).
Other meanings of "okres" that are not "time period" include "period" that women have and the one in physics.
I'd say that it was a lot too early to introduce this word and there just wasn't enough vocabulary to create more natural sentences.