χρόνον τάδ' ἦν τοσοῦτον ἔστ᾽ ἐν αἰθέρι μέσῳ κατέστη λαμπρὸς ἡλίου κύκλοσ

This is a line from Sophocles, Antigone 415ff. I came upon it in the syntax of W. Gunion Rutherford’s First Greek Grammar. I understand the whole passage he cites (after much furious flipping of the pages of the LSJ), but I am stumped by the two words τάδ᾽ and τοσοῦτον. I think that χρόνον is in the accusative to express extent of time. Does τοσοῦτον modify it? “so great a time”? And what about τάδε? Is it an adverbial usage? “thus”?

You’ve just about got it. ταδε is the subject. Lit “These things were for so great a time, until …”
That’s to say. This went on for a good while, till midday in fact, (when all of the sudden ….). The language is rather elevated, as messenger speeches tend to be.

I think I see it now. “These things” refers to what precedes.

Yes, that’s it. The guards were keeping watch over the corpse. As they were doing so, the sun’s orb blazed bright in mid-sky, as the day’s turning-point was reached (note κατεστη aorist not imperfect): it’s noon, a time with a touch of the supernatural about it.
The speech is a Sophoclean tour de force. I think it’s his best messenger-speech.

Many thanks.