I think I have a solution. I'm not sure if the Disabled method would work how you might want, another way to do this is to put a RemoteEvent ReplicatedStorage, and you'll Fire this to tell the script to spawn or not. Also a quick side note, if the zombie spawner is a server script, It should be in ServerScriptService, since im not sure if the scripts work there, and that might also be a problem. (Correct me if I'm wrong)
Here's what I mean:
Local script, In a gui
local Spawner = game.ReplicatedStorage.Spawn
local Time = 5
Spawner:FireServer(Time)
Server Script (Script), In ServerScriptService
local Spawner = game.ReplicatedStorage.Spawn
Spawner:OnServerEvent(Player, Time)
local Waiting = 0
repeat wait(
Waiting = Waiting + 1
until Waiting >= Time
end)
Going forward, If your creating any parts, using RemoteEvents really helps with communication between client and server. I hope this helps!