how do I make a script work for 120 seconds per person?

This can be achieved by tick(). This allows us to set a timestamp that we can compare time passed to. It would look like this:

local timeStamp = tick() --// Get's current time at the moment called.
local totalTime = 5 --// Time expected to pass
repeat wait() until (tick() - timeStamp) >= totalTime --// Compare time now to time passed.
print(totalTime.." Passed!")

Though this method above seems fancy, there is a totally simpler way, if you'd like to use this route. Just use wait(s)

print("Began")
wait(120)
print("Finished")

Hope this helps! If so, don't forget to accept this answer!

Try something like this:

local timeouts = {}

local function findHumanoid(part)
    if not part or not part:IsDescendantOf(workspace) then return end

    local current = part.Parent

    while current ~= workspace then
        local humanoid = current:FindFirstChildWhichIsA('Humanoid')

        if humanoid than return humanoid end

        current = current.Parent
    end
end

script.Parent.Touched:Connect(function(part)
    local humanoid = findHumanoid(part)
    if not humanoid then return end

    local player = game:GetService('Players'):GetPlayerFromCharacter(humanoid.Parent)
    if not player or timeouts[player] then return end
    timeouts[player] = true

    -- give them coins...

    -- set their timeout to false after 120 seconds
    delay(120, function() timeouts[player] = false end)
end)

Have a timeout variable for each player that stores whether or not they're not allowed to have coins. Set this to true and then, after 120 seconds or whatever your desired timeout is, set it to false and they'll be able to collect the coins again.