So how bad was the top edge of the glass when you de-rimmed that tank? I'm thinking of a top de-rim on a PetCo 40 if get one on $1 a gl it would become a riparium.
It's not the glass that is the hard part. It's removing the silicone. It usually only takes me about 20-30 min to get the rim off but up to 5-10 hours to get the silicone off, depending how perfect I want it. I don't do it all at once, I usually have just worked on it while dry starting. To be honest, I get most of it off in about 1-2 hours, it's just how much of a perfectionist you are.
I also do everything by hand, from the silicone to the edges. Some people use power tools and that would take less time but more room for error. I could get decent results in about 3 hours if I didn't mind some flaws.
If you are using razor blades and rubbing alcohol, like I do, let me give you one tip (besides using a bunch of fresh razor blades). Once you start getting the big parts of silicone off, take some 150 grit and bevel the edges slightly. It's not to put a bevel in the glass for looks. It prevents you from getting a bunch of tiny chips in the glass. If you don't, you get all these minor chips that can sand out by hand, but add a lot of time to the process.
It's not that hard, and a big reason it takes me so long is that I just do an hour per night or so.