Yes, it is too much. Chocolate has very tight working intervals. Dark chocolate must be used at 32°C. Below 30°C, it is too thick for use, and at 35°C, the cocoa butter separates from the chocolate. An error interval of 4°C when your complete workable interval is 5°C wide is simply unacceptable. You want a thermometer with a much higher precision, actually one which shows you tenths of degrees centigrade.
You also want a thermometer which reacts quickly enough. If you are working with small quantities, a ten seconds delay in measuring can give you errors of over half a degree centigrade, which is also a lot, given your tight working interval. Try finding a thermometer with a 4 sec response time or less.
Also, you don't want a laser thermometer at all! The difference in temperature between the surface of the chocolate and the mass of it near the bottom can be substantial, I once measured 4°C difference in something in a bowl with about a litter of stuff (it can't have been chocolate, probably it was custard, I forgot exactly). You need a candy thermometer for chocolate. Buy a laser thermometer separately for measuring the surfaces of pans, if you need it.
As a last note a 2°C interval is not 36°F, it is just below 4°F. The formula is 32 + 5/9, so your converter probably meant that when there are 2°C outside, a Fahrenheit thermometer shows 36°F. This is obviously incorrect for calculating intervals.
A couple of thoughts...
Not commenting on Valrhona specifically but 12h at 131F seems like a very long time at a very high temp. Can you temper it on its own at a lower temperature? Cooling the chocolate to 84F without contact to a cold(er) surface won't seed it well. You can also try adding rough shaved tempered chocolate in sufficient quantities during the 82F-84F state.
What is the cocoa butter content of the Van-Heusen? I don't know anything about it but if it is extremely low, you may be creating a low cocoa butter chocolate that is difficult to temper.
Take all of this with a grain of salt (please don't add any). I worked in chocolate for 10 years but haven't for the past 15 and I may be losing my mind. These are the steps I would take if it were up to me.
Best Answer
To answer the question as it stands, yes, you can overheat your chocolate and burn it, and that would be my concern if it was not as shiny as soon as you took it out and stirred it up. Usually you can tell because it will start to get a burned taste, but not always.
If it just wasn't shiny once it re-solidified, that's a pretty sure sign that your chocolate lost its temper. You can melt chocolate in a microwave without un-tempering it, and you can also re-temper it pretty easily. I learned how to do that by watching a How to Cook That video from Ann Reorden's website.
Basically, you don't want to heat the chocolate so much that it loses its temper in the first place. So when you heated the chocolate very slowly and gently, you didn't temper the chocolate, you just prevented it from losing its temper.
I usually get my chocolate too hot, though, like you did on your second try. When that happens, I find it easiest to throw another chunk of the same melting chocolate into the hot stuff and stir that around really well until the temperature is back in the proper range. Then remove what's left of the unmelted piece and use your tempered chocolate. This is one of the techniques explained in that video.
The temperature at which your chocolate loses its temper varies depending on the type of chocolate you use. Off the top of my head, for dark chocolate, you want to make sure it's only heated to 85-90 degrees throughout. For milk chocolate, the temperature range is even lower, and white chocolate is lower still.
So it's not a matter of heating too quickly, but of over-heating. And as long as you don't burn your chocolate, you can actually fix it pretty easily if you have a thermometer.