Countdown After Effects CC 2017

What exactly are you have a problem with?  Is it that you don't know how to use the numbers effect, or that you don't know how to apply the track matte?   You have to tell what you're trying to do and how you're trying to do it.   When you say it won't work the "way you need it to", we are supposed to know what you "need"?

In the basic use of the effect:

Apply the numbers effect to a solid.

Choose font and style, etc.  (you can change this after the fact by clicking options in the effect panel)

Set the number of decimal places you want

Set the size/position/color etc.

Set the value to where you want the count down to start.  KEY IT

Move the cti forward in time to where you want the countdown to end.

Set the value to the what you want it to end at (you should now have two keyframes)

It's not really a complicated effect.

If it's the track matte you can't figure out that's an entirely differnet issue and you're going

to have to provide details about your project, layers. etc

I doubt very much if that effect has been updated in the last decade, it's an oldie.  They are on to bigger and better things.

That also means you won't find anything new on tutorials, me thinks.  Lynda.com has a tutorial older than your computer(and Jesus, Mary and Joseph that's old, I think the Smithsonian is looking for one)  where Chad Perkins walks through all of the effects, to my mind it's a pretty simple effect, at least going up, which is the only way I've used it.  I'm sure it is covered in that series, and he is a hoot to watch.