I have tried to temper equal amounts of Valrhona Couverture Manjari (64%) chocolate + baking chocolate (Van-Heusen brand, dark chocolate) without any success. 

Used the seeding method & followed the instructions given by Valrhona, ie melt @ 131-136F, cool to 82-84F, reheat to 88-90F. Working with a very small batch (~400g), used a bain-marie, IR thermometer. 

The chocolate is nice and shiny but simply does not harden at room temperature. 

Valrhona instruction says it needs to be melted for 12h but I have read articles where others have been able to temper without melting for 12h. 

I have no clue what's going wrong. Would be grateful for any guidance.

Thanks in advance.
Asha