The HD resin isnt very stable. Its very thick too, like syrup. You spend a ton of time trying to get it to soak into what youre glassing. Very hard to work with. My first 10 times glassing I used the HD stuff, and thought all was well. Then someone told me to try a different resin. I bought the stuff they recommended and it was night and day. My projects looked 1000000x better and took 1/2 the time.
Look for a boating or fiberglass supply company. The HD resin is like a brownsh/greenish with a very distinct smell and the consistency of a thick syrup. The good stuff is very thin, like a very hot syrup, and is pink. Also smells very different. It will be much more stable (for x amount of drops, it will last X amount of minutes... Every time). But just going by the recommended mix rate, you should be just fine with the new stuff, since you wont spend half your time working the resin into the material.
If you cant find any locally, check this out. Ive heard great things about this, the 404 polyester resin.
Polyester Resins
Also, if youre trying to resin big pieces and you have an open area and a spray gun (I had the Second Skin Spectrum spray gun to shoot the thick deadener), you can always spray this resin. I resined the outside of my box to make it waterproof (it was a blowthrough) and it was much easier to just spray a few nice, quick, thin coats of resin with a TON of hardener in them than to mix it cool where you need a bunch of time to brush it on.
Everyone is saying not to use a lot of hardener, just be careful with that. Eventually, a single drop of hardener will cure most any amount of resin, but it will take ages. Ive mixed it so cold where it was sticky for weeks and had to throw projects away because it was tacky and not completely cured for so long. I always mix really small batches pretty hot, where I have 10 mins of work time and then just dip the brush in acetone when it starts to harden. This way, Im not waiting forever.