But I think I may have not used enough hardener or mix it well enough as it didn't harden in half an hour. But it is about 50s outside.

I know when you put too much hardener it hardens FAST and almost not enough time to work with (and if the weather is hot, you have about 5 minutes to work with it before it skin over)

I was wondering if it will harden on its own without enough of the hardener??? it doesn't seem like it was as critical like mixing epoxy.

I have had it work at wide ranges of mix, so I think it will eventually harden unless you are way off on the ratio.

It participates in starting the polymerization reaction, but is not actually consumed as a reactant.

The easiest way to use the filler is to get it on the surface as quickly as possible, then wait for it to slightly harden.

At that point sharp chisels and cutters can be used to remove any large amounts required, with some final work and sanding after it fully hardens.

I use it to repair painted molding all the time.
Even window muntins damaged by moving a double hung with the lock party closed can be repaired.

Fill the gouge to over full, allow to partly harden, shape with carving chisels, allow to finish hardening, clean up again with chisels (and even shoulder planes) and then a little sanding.

Instruction said to follow with High performance filler that's when I ask this question, I just wanted a skim coat on this area to protect what's left of the wood.
Day 1 in warm afternoon failed miserbly, after I put on a small test patch I decided to put the hardener all of it directly into the can, BIG MISTAKE, it was not usable within 5 minutes.
So I attemped this morning at 50F. Mixing a couple
dallops at a time I wasn't fun and I wasn't sure if I got a good mix. At least not when you are up there just before sun rise and cold.. Let's just say I have some hardener left after the can is gone.

But when I went home about 12 hours later it has hardened real well. (was getting worried I have created the biggest mess ever) Since it was thick to work with so there was some rough knock down texture but I will have to flatten it with sand paper now and 2 coats of paint.

I am not sure if it will crack later but I think it will buy me more time than just a coat of paint. The wood really stiffened alot and now shielded from the sun. There may be some water issues contributing to the decay of the siding but since it was only the west side I think it is mostly sun damage.

I noticed some in the neighborhood have vinyl siding but only around the chimney, so maybe what I will do down the road.

Also please don't buy Elmer's wood restore kit unless you are repairing a hole, it is totally different texture (like playdoh instead of paste) and does not stick to the wood. It's only good to push it into a hole you can't really spread it with a putty knife.

The 'golf ball' size recommendation on the can is really needed.

If I need a lot of material I use aluminum foil to line the minwax cover so clean up for the next batch is easy.

As long as the material has hardened it sands very easily (about like soft pine).

The wood hardener is acrylic resin in a solvent, and does work well.

I routinely use it to treat the end grain of exterior trim to prevent water absorption.

A friend had some 1x corner boards rot within 2 years.
We replaced them and treated the ends with hardener.
He has had to repaint once in 12 years and the wood is still solid.

Acetone is likely to damage that siding.