Not much earlier. The earliest tmk is at the Grand Tribunal in 832.
You can look up GotF p.113 box The Order of Odin, HMRE p.121 box The Order of Odin and in AM p.133ff The Order of Odin, there especially p.135 The Viking Invasions:
Starting in about 830, the Vikings led a major assault against Ireland, <...>
It was there that the Scandinavian rune wizards first encountered representatives of the Order of Hermes, in the form of a group of Diedne magi from a covenant several miles northwest of their camp. <...>
the magi realized that they were unusually vulnerable to these attackers, and
they were troubled. They brought word of these strange northern wizards to the Grand Tribunal of 832, where those who had heard of their pagan faith and their Anglo-Saxon kin dubbed them members of “The Order of Odin.”
In 837 a delegation of primarily Irish magi from many different Houses, led by Máel-tuili of Merinita, sought out the rune wizards and attempted to parley with them. At first, the Viking leaders were abusive and demanded to know their secrets, but after hours of negotiation the rune wizards eventually agreed that
they would leave in peace if the magi paid to them a tribute of 3,000 pounds of silver and forty pawns of vis. This price was arranged, but soon after they had it in hand the Vikings reneged on the deal and attacked. The leaders of both parties fell in the subsequent battle, and many other magi and wizards were killed. The news of this betrayal stirred equal parts of outrage and horror in the local magi and throughout the Order, but no immediate action was taken.
But you should read F&F p.67f Castra Solis completely, indeed. Here's what I consider the central part about when the Hermetic legend of the Order of Odin really took hold:
Between 840 and 850, attacks on local villages increased, and certain isolated
magi living in the interior of Gascony complained at Tribunal. By 850, the Flambeau magi of the region incorrectly believed that the so-called Order of Odin had reignited a war through the sudden series of raids on the western coast. They mistook the individual vitkir supporting their clans and relatives for members of a larger organization, all sharing an aggressive and unified vision, finding an enemy where there were merely raiders. Wrongly convinced of the scope of this danger, Kaeso returned to Bordeaux to fortify his temple with the full support of House Flambeau and his Hoplites. <...>