[Lee N. Field]

What date would that have been? Acts 21 occurred no earlier than 56 CE.

40 years, roughly, from the death, resurrection and ascention of Christ, to the siege of Jerusalem and destruction of its temple.

[Tzfat]

So, since a date is not forthcoming, perhaps there is an event that indicated that, as you said, "Old (Mosaic) Covenant cultic order was pretty thoroughly ended."

One would think that since the model of following by example is replete through Scripture, Luke would have made it clear that although Paul, James, and "myriads" of followers were an exception that those that read should not follow.

There are multiple places in the Prophets that specifically about a return to Temple worship. Specifically, Zechariah 14, Ezekiel 44-48.