Got it all working

src/data/clearlag/functions/clear_items.mcfunction

@@ -1 +1,2 @@
-kill @e[type=item]
+kill @e[type=item]
+say @a "Clearing items..."

src/data/clearlag/functions/load.mcfunction

@@ -1,3 +1,4 @@
 scoreboard objectives add cl_timer dummy
-scoreboard players add timer cl_timer 0
-scoreboard players add timer_goal cl_timer 6000
+scoreboard players set timer cl_timer 0
+scoreboard players add timer_goal cl_timer 0
+execute if score timer_goal cl_timer matches 0 run scoreboard players set timer_goal cl_timer 6000

src/data/clearlag/functions/reset.mcfunction

@@ -0,0 +1 @@
+scoreboard players set timer cl_timer 0

src/data/clearlag/functions/tick.mcfunction

@@ -1,2 +1,2 @@
-scoreboard players add cl_timer cl_timer 1
+scoreboard players add timer cl_timer 1
 execute if score timer cl_timer = timer_goal cl_timer run function clearlag:timer_out

src/data/clearlag/functions/timer_out.mcfunction

@@ -1,3 +1,2 @@
-scoreboard players operation timer cl_timer = timer_goal cl_timer
+function clearlag:reset
 function clearlag:clear_items
-say @a "Clearing items..."

src/data/minecraft/tags/functions/load.json

@@ -1,3 +1,5 @@
 {
-    "values": ["timer:load"]
+    "values": [
+        "clearlag:load"
+    ]
 }

src/data/minecraft/tags/functions/tick.json

@@ -1,5 +1,5 @@
 {
     "values": [
-        "timer:tick"
+        "clearlag:tick"
     ]
 }