1) In normal in game chat type the following commands:

/scoreboard objectives add Timer killedByTeam.dark_green
/summon minecraft:armor_stand ~ ~ ~ {NoGravity:1b,Invulnerable:1b,Marker:1b,Invisible:1b,Tags:["BlockDestroyer"]}
/effect give @e[type=minecraft:armor_stand,tag=BlockDestroyer] minecraft:regeneration 1000000 127 true
/scoreboard players set @a Timer -1
/scoreboard objectives add IsSpreader killedByTeam.aqua
/scoreboard players set @a IsSpreader 1
/scoreboard players set @e[type=minecraft:armor_stand,tag=BlockDestroyer] Timer 0
/scoreboard objectives add YValue killedByTeam.dark_blue
/scoreboard players set @a YValue -1
/scoreboard players set @e[type=minecraft:armor_stand,tag=BlockDestroyer] YValue 0

2) Place down a repeating command block, facing upwards (unconditional, always active) with a chain command block, facing upwards (unconditional, always active) above the repeating command block.

In order to make sure that the timer works in the repeating command block put in the command:
scoreboard players set @e[scores={Timer=61..}] Timer 0

In the chain command block put in the following command:
execute as @e[scores={Timer=0..}] run scoreboard players add @e[scores={Timer=0..}] Timer 1

3) Now place a chain command block, facing upwards (unconditional, always active) above the one you just placed. Put in the following command:
execute at @r[scores={IsSpreader=1}] run spreadplayers ~ ~ 0 3 false @e[type=minecraft:armor_stand,tag=BlockDestroyer,scores={Timer=30}]

Then, place a chain command block, facing upwards (unconditional, always active) with the command:
execute at @e[scores={Timer=40}] run scoreboard players add @e[scores={YValue=0..}] YValue 1

And another chain command block, facing upwards (unconditional, always active) with the command
execute as @e[scores={YValue=7..}] run scoreboard players set @e[scores={YValue=7..}] YValue 0

4) Now place 7 chain command blocks, all of them facing upwards (unconditional, always active) put in the following commands, starting from the lowest one and ending at the highest one you just placed:

Lowest Chain Command Block:
execute at @e[type=minecraft:armor_stand,tag=BlockDestroyer,scores={YValue=0,Timer=60}] run setblock ~ ~-3 ~ minecraft:air replace

2nd to lowest Chain Command Block:
execute at @e[type=minecraft:armor_stand,tag=BlockDestroyer,scores={YValue=1,Timer=60}] run setblock ~ ~-2 ~ minecraft:air replace

3rd to lowest Chain Command Block:
execute at @e[type=minecraft:armor_stand,tag=BlockDestroyer,scores={YValue=2,Timer=60}] run setblock ~ ~-1 ~ minecraft:air replace

Middle Chain Command Block:
execute at @e[type=minecraft:armor_stand,tag=BlockDestroyer,scores={YValue=3,Timer=60}] run setblock ~ ~ ~ minecraft:air replace

3rd to highest Chain Command Block:
execute at @e[type=minecraft:armor_stand,tag=BlockDestroyer,scores={YValue=4,Timer=60}] run setblock ~ ~1 ~ minecraft:air replace

2nd to highest Chain Command Block:
execute at @e[type=minecraft:armor_stand,tag=BlockDestroyer,scores={YValue=5,Timer=60}] run setblock ~ ~2 ~ minecraft:air replace

Highest Chain Command Block:
execute at @e[type=minecraft:armor_stand,tag=BlockDestroyer,scores={YValue=6,Timer=60}] run setblock ~ ~3 ~ minecraft:air replace