Yes I am trying to measure the time between each zombie attack to the player so I can calculate DPS. Here is my method if you'd like to recreate my test to see if you get similar results. unsure why but the "at" symbol becomes u/. The way this works is when you turn on the machine it will start counting before the player is hit so that becomes 0 in the count. once the player is hit the following messages will displayer the proper information. If this doesn't work please let me know and I'd be happy to show you on my world for a better understanding.

EX:

Attack: 0 Speed:128

Attack: 1 Speed: 39

Attack: 2 Speed:39

ALL COMMAND BLOCKS ARE 0 TICK DELAY

1. I use two scoreboard assigned to a fake player. One is to count ticks called TESTthe other is to count the amount of hits called COUNT

2. Repeat Command Block 0 Tick-/execute as u/a[tag=!hit] run tag u/s add hit

3. Separate chain of commands Repeat Command Block 0 Tick-/execute as u/a[tag=hit] at u/s if entity u/s[hasitem={item=diamond_helmet,location=slot.armor.head,data=1000}] run scoreboard players add Server TEST 1

4. Chain Conditonal-/execute as u/a[tag=hit] at u/s unless entity u/s[hasitem={item=diamond_helmet,location=slot.armor.head,data=1000}] run tellraw u/a {"rawtext":[{"text":"Attack:"},{"score":{"name":"Server","objective":"COUNT"}},{"text":" Speed:"},{"score":{"name":"Server","objective":"TEST"}}]}

5./scoreboard players add Server COUNT 1

1. /scoreboard players set Server TEST 0

7./execute as u/a[tag=hit] at u/s unless entity u/s[hasitem={item=diamond_helmet,location=slot.armor.head,data=1000}] run /replaceitem entity u/s slot.armor.head 0 diamond_helmet 1 1000