First when the script is fully done, you can touch again?

First when its been on transparency = 1 you can touch again.

local p = script.Parent
local t = "5"

function Ontouch()
	p.Transparency = 0.1
	wait(t)
	p.Transparency = 0.2
	wait(t)
	p.Transparency = 0.3
	wait(t)
	p.Transparency = 0.4
	wait(t)
	p.Transparency = 0.5
	wait(t)
	p.Transparency = 0.6
	wait(t)
	p.Transparency = 0.7
	wait(t)
	p.Transparency = 0.8
	wait(t)
	p.Transparency = 0.9
	wait(t)
	p.Transparency = 1

end

p.Touched:connect(Ontouch)

What you want to add is called a 'debounce':

local p = script.Parent
local t =  5 --You can't wait "5". :P

local deb = false --Our debounce variable

function Ontouch()

	if deb then return end --Don't do anything if debounce is on!
	deb = true --Turn it on otherwise...

	for i = .1, .9, .1 do --To avoid repetition
		p.Transparency = i
		wait(t)
	end
	p.Transparency = 1

	deb = false --Now that we're done, turn debounce off!

end

p.Touched:connect(Ontouch)

local p = script.Parent
local t = 5
local defaultTrans = 0 -- plug in the number you want the block's transparency to revert to

local touchable = true 

function Ontouch() -- I made the logic more compressed, and faster to write and go through/edit
	if touchable then
	p.Transparency = defaultTrans 
	touchable = false
		for i = 1, 10 - (defaultTrans * 10) do
			p.Transparency = p.Transparency + 0.1
			wait(t)
		end
		touchable = true
	end
end

p.Touched:connect(Ontouch)

I hope this helped :D