I am utterly perplexed by this sentence, no Pole would use it as a greeting. The only reasonable translation is “a good day”.
Well, perhaps you could say it ironically, or if you wanted to allude to the standard Czech or Slovak greeting (dobrý den / dobrý deň). I think you can go ahead and flag it next time you encounter it.
The standard “dzień dobry” is used throughout the day, so it corresponds to both “good morning” and “good afternoon”. In the evening, we usually switch to “dobry wieczór”.
Come to think of it, it’s a bit weird that the word order is reversed in the daytime greeting, but not in the evening greeting.