curious about how CLEAR works [duplicate]

As I understand it, CLEAR is a service that'll let you skip to the front of the line. To get it you have to go to an enrollment center and have your biometrics taken. It's my understanding that this visit to the enrollment center does not need to be scheduled.

I have a few questions about how it works.

Can I just get to the airport early and do it before my flight? Or would I be better of taking a half day of vacation and taking care of it, myself, a few weeks before the flight?
Does CLEAR work at all hours? Like let's say I have a flight that departs the airport at 11pm. The airport in my hometown does have a few scant flights that depart at that time but, by and large, all the shops are closed and TSA is basically a skeleton crew at that point. If it wouldn't work then at what times would CLEAR work? Is there a website that'd list the hours for CLEAR?
There are a few promo codes for CLEAR floating around the internet. https://thepointsguy.com/2017/09/why-you-should-have-clear/ has two. idk if they're still valid (the post I linked to is over a year old) but let's say they are. Can I use them if I choose to register in-person as opposed to online?
What if my trip isn't for six more months. How soon before the trip should I register? Like if I register right now - a full six months before my trip - could I still get my biometrics taken when I'm at the airport about to catch my flight or will I need to get my biometrics taken before?

Thanks!