They're all May 7th.
23rd: Age 756.
24th: Age 767, 11 years later (5 days before the Androids appear).
25th: Age 774, 7 years later.
26th-28th: 778, 781, 784.
I always thought they had a break after the 23rd because it was too crazy. If it had happened 3, 4 or 5 years after the 23rd (Age 759, 760 or 761), it would have been during peace (Raditz arrived October 760, but he barely caused a stir). If it had happened after 6 years (Age 762), it would have been during the training to fight the saiyans, so I guess many of the famous fighters would be absent, which could have put them off. The years after that were basically peace again and even the destruction Nappa created wasn't any worse than what King Piccolo did before the 23rd budokai. So I think they were just scared of the 24th being too dangerous or maybe they had no fighters available (because they didn't want to enter after seeing the 22nd-23rd tournaments), so they had to wait for a new generation of fighters to emerge.
The 7 years between the 24th and 25th it's harder to think of a reason, but maybe Mr Satan was just milking his fame and got it postponed somehow.