We know that Boaz introduced the possibility of greeting people using the tetragrammaton. The Mishnah in Berochos 54a says
והתקינו שיהא אדם שואל את שלום חברו בשם שנאמר והנה בעז בא מבית לחם ויאמר לקוצרים ה' עמכם ויאמרו לו יברכך ה' ואומר ה' עמך גבור החיל
and they instituted that one should greet his friend using the tetragrammaton as it says “Presently Boaz arrived from Bethlehem. He greeted the reapers, “The LORD ( tetragrammaton) be with you!” And they responded, “The LORD ( tetragrammaton) bless you!” and it says “The Lord ( tetragrammaton) is with you mighty man of valour”.
And Rashi comments
שיהא אדם שואל לשלום חבירו בשם. בשמו של הקב"ה ולא אמרינן מזלזל הוא בכבודו של מקום בשביל כבוד הבריות להוציא שם שמים עליו ולמדו מבעז שאמר ה' עמכם ומן המלאך שאמר לגדעון ה' עמך גבור החיל:
That a person should greet his friend using the tetragrammaton: with the name of the Holy One Blessed be He and we do not say that this denigrates the honour of Hashem in order to honour humans and we learnt if from Boaz who said “The LORD ( tetragrammaton) be with you!” and from the angel that appeared to Gideon and said “The Lord ( tetragrammaton) is with you mighty man of valour”.
I do not know of a source about the use of the tetragrammaton for any purpose before Boaz.
According to Wikipedia based on Encyclopedia Britannica (is this an accepted source for us?)
Some time after the destruction of Solomon's Temple, the spoken use of God's name as it was written ceased among the people, even though knowledge of the pronunciation was perpetuated in rabbinic schools. Philo calls it ineffable, and says that it is lawful for those only whose ears and tongues are purified by wisdom to hear and utter it in a holy place (that is, for priests in the Temple). In another passage, commenting on Lev. xxiv. 15 seq.: "If any one, I do not say should blaspheme against the Lord of men and gods, but should even dare to utter his name unseasonably, let him expect the penalty of death."
In which historical periods was it allowed to pronounce the tetragrammaton? From the sources above it seems that there was a time when it was permitted to be spoken and later even to be used in a greeting. Later still it was forbidden.
(Was Abba Shaul the one who forbade it? For as we know, the Mishnah in Sanhedrin 10 (1) lists those who have no share in the World to Come. Included in these according to Abba Shaul is someone who utters the Divine Name as it is spelled.)