Understandable though I feel I must point out that technically by the wording they may encounter up to 7 or 8 encounters! (Even though the tower is 6 miles away “if mounted, the party should arrive within seven hours. If walking, it should take eight hours.” and that you should roll on the desert encounter table every hour of travel.
a) I think that’s far too many encounters; even upwards of 6 is too many in a row, even if they’re not all combat, but since they’re all random you have no control over if they are. My suggestion: Roll for an encounter check on a d6 each hour. If that was the intention no worries.
b) I also think the discrepancy between walking and mounted should be greater than an hour. Mounts usually cut the walking travel time in half, otherwise the cost of them wouldn’t be worth the modicum of savings in travel time.
Sorry, I’m not trying to nitpick, I just want to provide constructive feedback. There’s good stuff here, let’s just polish up the rest. :)