It's time for lunch would idiomatically be something like "ήρθε η ώρα να φάμε μεσημεριανό" (it came the hour for us to eat lunch). For instantaneous time you us

It's time for lunch would idiomatically be something like "ήρθε η ώρα να φάμε μεσημεριανό" (it came the hour for us to eat lunch). For instantaneous time you use hour (ώρα) or στιγμή (moment). So there's actually three "temporal terms" in Greek, ώρα, χρόνος and καιρός. In my head καιρός is the "longest" of the three (describing a period rather than an instant), and ώρα and χρόνος are sort of depending on context. Ώρα is used in contexts like "δεν είναι η κατάλληλη ώρα για αυτό" (it's not the right time for that), where you could replace it with "moment" in english (στιγμή). Χρόνος is the least frequently used in the modern language I would say, and is mostly associated with abstract notions of time as a concept (e.g. "the passage of time") but also in specific terms like "I don't have time for that" (δεν έχω χρόνο για αυτό). All of these words overlap somewhat so it gets somewhat confusing to describe to a non-native speaker, other than saying that generally a native speaker will be able to tell if the use of one of the three "feels right" in a certain context or not. Also several of these terms have additional meanings! For example, ώρα is also literally hour (είναι τρεις η ώρα = it's three o'clock, literally "3 is the hour"), χρόνος also can mean "year" (για έναν χρόνο = for one chronos = for one year), etc. etc.