24 July 2009: death of Harry Towb, who gets killed off by the Ice Warriors as Osgood in The Seeds of Death (Second Doctor, 1969) and by the Master as McDermott in Terror of the Autons (Third Doctor, 1971). As McDermott he uses the best Ulster accent ever heard on Old Who (there have been a couple in New Who who were at the same level). Here he is, dying twice.
ii) broadcast anniversaries
24 July 1965 - broadcast of 'Checkmate', the fourth episode of the story we now call The Time Meddler, ending the original second season. The Monk reveals his plans to equip Harold Godwinsson's army with atomic bazookas to change history. The Doctor outwits him and sabotages his Tardis. Closing titles play over arty shots of Steven, Vicki and the Doctor against a starry background.
24 July 2010: First perfomance of that year's Doctor Who at the Proms.
iii) date specified in-universe
24 July 1794: Setting of much of "Guests of Madame Guillotine", the second episode of the 1964 First Doctor story we now call The Reign of Terror.
24 July 1989: the Sixth Doctor meets Mel Bush for the first time, in Gary Russell's 1997 novel Business Unusual.
24 July 6012: Setting of The Doctor's Daughter (Tenth Doctor, 2008).