I was wondering, what is Forgiveness Sunday like in Greece? What time is it usually? Do they prostrate?
It's not called "Forgiveness Sunday" in any of the ancient patriarchates or the Church of Greece to my knowledge. It's called Κυριακὴ Τυρινῆς (and whatever that is in Arabic), which means Cheesefare Sunday basically.
That Sunday evening (not actually Sunday liturgically) is the first time a "κατανυκτικὸς Ἑσπερινός" (solemn Vespers) is served. In my experience in Greece, many parishes and certainly the monasteries serve the solemn Vespers every single night of Great Lent. It has a modified structure determined by the Triodion, including the famous difference in the ending with the short hymns and the prayer of St. Ephrem.
The very first time the solemn Vespers is served it is called the solemn Vespers of Forgiveness (ὁ κατανυκτικὸς Ἑσπερινός της Συγνώμης). According to the Typikon itself, the people approach the priest and receive his forgiveness. That's all that's said. This is unusual, since in the Byzantine tradition, the priest does not offer blessings with a blessing cross or any other means after a typical Vespers. The priest retreats behind the iconostasion, the curtains are closed, the people venerate the Icons in the front of the church and then leave. That's what I've seen even in Slavic and Romanian monasteries/sketes on Mt. Athos. I'm not sure where the whole blessing cross after every single service comes from.
Anyway, there is no mention in the Typikon of if or how the people should ask forgiveness of each other.
Finally, in terms of popular piety, I would say Clean Monday is generally seen as a much bigger deal than the solemn Vespers of Forgiveness.