Can I pin myself if I’m on PCs leave? Or should I wait to arrive at my new unit?

I’d advise you wait until you arrive at your unit. In the mean time, let your sponsor know you made the cut off and to inform your COC. If you a copy of your promotion orders that would be helpful and you should send a copy to your sponsor or gaining unit S-1. I would definitely advise against pinning yourself. The transition from SPC/CPL to SGT usually comes with an NCO induction ceremony. You really don’t want to start off on the wrong foot with your new unit CSM. Good luck and congratulations.

The orders are what matters. The ceremony is just a tradition. Being on the list doesn't mean you are promoted yet as well. If you have promotion orders and it is past the date of rank, then throw it on. If you are still just "promotable" then continue to wait for points.
I pinned SFC without a ceremony. Ceremonies are nice and all, but it is the orders that actually promote/award/assume command

In line with MSG (Join to see) and MAJ (Join to see), I would advise against doing so without gaining unit permission. Some folks get SUPER touchy about it.

I picked up SFC while I was in school. Technically, I was TDY from Florida to Fort Huachuca. However my assignment in Florida was actually a detachment from a parent company in.... you guessed it, Fort Huachuca. My parent unit pinned me on a Friday evening after the schoolhouse was done with me. The schoolhouse unit was PISSED and the 1SG ripped off my rank when I showed up with it Monday morning. I explained that my ACTUAL unit had pinned me, not just me pinning myself, and not my TDY unit (the schoolhouse). He refused to find that an "acceptable answer" and threatened to make me wear SSG for a week as "punishment."

To be clear - that was completely unprofessional of the 1SG, and there is no way he could have enforced his threat. But it didn't stop him from blowing a gasket. Even though I didn't pin myself, that 1SG *still* felt like I was trying to "cheat him out of my promotion" (his words). Not sure how he was entitled to *my* promotion, but that is how he felt.

I am not saying that reaction is routine or to be expected - but I am not saying he is the only 1SG who ever had that thought process, either. Better to be safe. If you want family to be there, participate, or even do it themselves, most of the time the unit - gaining or losing - will be happy to accommodate. Just don't leave them in the dark.