Distances and travel time
Thirty English miles could be covered in four days - see Vulgate VI, where Lancelot and Ector, four days before Lancelot must be at Camelot to fight for the Queen, pass the night at Alphin castle, thirty English miles from Camelot. (One can suspect, however, that, at need, thirty English miles could be covered in a much shorter time than four days.)
Also according to the Vulgate VI, Arthur and his army reached Joyous Garde on the second day after leaving Camelot, after one overnight stop. The Vulgate , however, makes Camelot distinct from Winchester (in flat contradiction to Malory). Nevertheless, Camelot appears reasonably near Winchester even in the Vulgate. Thus, from the vicinity of Winchester to the Humber, the distance could be covered in less than two days. Even allowing for the fact that this may have been a forced march, such speed makes identification of one site by its distance according to days' travel from another exceedingly chancy.
Sir Persant's city was seven miles from Castle Dangerous. Gareth offered to be finished with Persant "within two hours after noon ... [a]nd then shall we come to the siege [of Castle Dangerous] by daylight." Gareth presumably meant that he would also have time to fight the besieging champion by daylight. The season was late spring of early summer - a few days after Whitsuntide, so that the days would have been fairly long. As it turned out, Gareth and Lynette stopped for the night with Persant, but Gareth's statement may help indicate normal traveling time on horseback.
Six miles was considered a reasonable distance to travel to hear Mass. Presumably, traveling six miles for this purpose was permissible on a Saturday or Sunday, even though other travel was frowned upon the Sabbath. Gawaine was once admonished by a friar for riding late on Saturday; the knight swore not to do so again unless it was unavoidable.
Then ... on foot they yede [traveled] from Glastonbury to Almesbury, the which is little more than thirty mile. And thither they came within two days, for they were weak and feeble to go.
Normal traveling time on horseback from Georgia to New Orleans (550 miles) was 13 ˝ days in the middle of the nineteenth century. A horse named Paddy, ridden by Sam Dale with a vital message, is cited for covering the distance in 7 ˝ days, cutting six days from the normal travel time. On the other hand, in a feature article printed in the "Chicago Sun-Times", April 12, 1978, Dennis Waite describes trying to hike from Llanberis, Wales, to the summit of Mount Snowden, three and a half miles on a dirt road. Waite's landlady claimed the walk was "two hours up and one hour back", but an English couple Waite's party met as the Americans finally turned back in discouragement said the walk, roundtrip, took a full day. Obviously, time spent in traveling from place to place in the Arthurian landscae depends on type of terrain - forested, mountainous, and so on - as well as on type of locomotion (horse, mule, wagon, foot) and availability of roads (many of the old Roman roads, like the famous Watling Street, would naturally have been available to Arthurian travelers).
When it was necessary or desired, messengers and pursuivants could carry news quite rapidly - as we think of news as spreading in those days. Gareth defeated Ironside and raised the siege of Castle Dangerous shortly after Pentecost. There followed a few extra adventures which must have taken up to a week. Arthur and Lyonors then decided to have a tournament at Castle Dangerous at Assumption, in mid-August.
And so the cry was made in England, Wales, and Scotland, Ireland, Cornwall, and in all the Out Isles, and in Brittany and in many countriess; that at the feast of our Lady the Assumption next coming, men should come to the Castle [Dangerous] beside the Isle of Avilion[:] ... And two months was to the day that the tournament should be.
Two months for the messengers to cover all that area and still leave the interested knights in time to see to their preparations (though they seem to have kept ready for knightly adventure throughout the warm seasons) and travel to Lyonors' castle from those distant countries!
One further note: romance accounts of time spent in travel need not always be taken literally or seriously. Harris, commenting on a passage in Chrétien's Yvain, theorizes that Chrétien may have been poking fun at the speed of characters' travel in old romances.