Run a command block once every day

First I would summon an armor stand to keep count of a scoreboard.

/summon armor_stand ~ ~ ~ {Invisible:1b,Invulnerable:1b,NoGravity:1b,CustomName:'{"text":"timer"}'}

Then I'd create a timer scoreboard.

/scoreboard objectives add timer dummy

Have a command block add 1 to this every tick.

/scoreboard players add @e[type=armor_stand,name=timer] timer 1

And calculate the time you want in ticks (20 ticks/s). For 1 real life day that would be 20x60x60x24, which is 1.728.000.

Then place the block exactly 1 tick before the timer is at the right time.

/execute if entity @e[type=armor_stand,name=timer,scores={timer=1727999..1727999}] run setblock ~ ~5 ~ minecraft:diamond_ore destroy

And then reset the score at the correct time.

/scoreboard players set @e[type=armor_stand,name=timer,scores={timer=1728000..}] timer 0

This should place/destroy the block every 24 hours. If you want minecraft days, they are 24.000 ticks instead of the 1.728.000.