[Mithalwen]

Glorfindel had left Rivendell nine days before he met the hobbits and Aragorn however they had travelled by slow routes and later with a gravely ill Frodo. It is 348 mile from Bree to Rivendell andso not far short of 400 from Woody End even as the crow flies which is more direct than even an elf must run . Frodo met Gildor on the night of the 24th Sept and Glorfindel leaves Rivendell on the 9th of October so there is a maximum of two weeks if Glorfindel left on the day the news arrived. I think that an average of 28 mile a day is eminently "doable" for swift and tireless elven feet - the three hunters managed 135miles in four days. And the message may have been relayed because of reference to the travelling companies. However they may have used Osanwe Kenta, a kind of elvish telepathy. It isn't like picking up a telephone - communication depends on the skill and degree of affinity of the communicants as well as distance. I can't find a suitable link and unfortunately it is an essay that hasn't been published in a widely available format.