Func_button_timer help

An explanation first: So I had an idea at work the other day while I was trying to distract myself from the grueling grind, and I thought up a map idea. So basically, it’s another wave map, because there will never be enough of those, but it is more complicated than just setting up waves. It will have a currency system and you can buy units/defenses/whatever. The more and more I thought about it, I remembered a L4D2 map named Convoy, which had basically the same set up.

The thing I need help with is replicated the func_timed_button from the L4D games inside of Garry’s Mod.

I think you can use this as a substitute:

It’s used for those valves you rotated in HL2, where you have to hold down E on them for a certain time or they’ll reset.
You could use that, but make it invisible, and experiment with rotation distance to get the time you want.