Games : this double jump mechanic doesn't work

this double jump mechanic doesn't work I've just asked a question but one of the answers by ModDL seemed like it should work this is what it was

also could some one give me a pic of a 20 tps clock I am not to Shure what it is

Scoreboard Setup:

/scoreboard objectives add LivingTime dummy

Clock (20 tps clock):

/execute @a ~ ~ ~ detect ~ ~-2 ~ air 0 summon ArmorStand ~ ~ ~ {CustomName:Target} /execute @e[type=ArmorStand,name=Target] fill ~-2 ~-1 ~-2 ~1 ~-1 ~1 barrier 0 destroy /scoreboard players add @e[type=ArmorStand,name=Target] LivingTime 1 /execute @e[type=ArmorStand,name=Target,score_LivingTime_min=20] fill ~-2 ~-1 ~-2 ~1 ~-1 ~1 air 0 destroy /kill @e[type=ArmorStand,name=Target,score_LivingTime_min=20]

First command summons a Armor stand with a custom name of Target at every player who has a air block 2 blocks below him. Secondly, it fills the area 2 blocks below every armor stand that has a custom name of Target. Then the LivingTime for every Armor stand is ticked up and when the armor stand is ticked 20 times the area 2 blocks below is replaced by air and the armor stand is killed. thanks mr_assley19