I'm crazed about the temperature of the warmed liquid (milk in this case) used to activate yeast. My friend Donna Currie recommends 105-110 degrees F for dry yeast. I used an instant read thermometer to gauge the temperature, but if you're a good judge of temperature, you can judge the heat by putting a few drops of the milk on your wrist.
I made the chocolate tahini filling on the first day, just after I put the dough into the refrigerator. That meant it was rather hard when I removed it from the refrigerator. I microwaved it on a low setting in 30 second increments until the filling loosened. You can make it then, or wait until the next morning.
For melting chocolate, I use microwave the chopped chocolate on a low setting in 30 second increments, stirring after each increment, until the chocolate is thoroughly melted and smooth. If you melt the chocolate on the stovetop, either use a double-boiler (a pot of simmering water with a smaller post of chopped chocolate on top, so that the chocolate never touches either the water or the direct heat) or melt it on a very low light, stirring constantly to prevent burning.