Potion nightmares: Wideye.

What am I doing wrong? It always says I fail to keep it up to temperature.

The instructions are simple enough; 6 snake fangs and 4 standard ingredient into mortar, add 6 'stings into the cauldron, set it warming whilst I crush the stuff in the mortar so I can add it immediately after the 30 seconds is done, and then stir it, all the while ensuing that the temperature stays at medium. That bits pretty easy.

The bit I can't work out is the final stage, waving the wand. No mater what I do or what temperature the cauldron is when I select the wand, it ALWAYS switches the cauldron flame off and the wand wave takes so long that that it drops the temperature below the medium mark ruining the potion.

I gave up on trying the brew them when I first got into Pottermore because of this. Any potion masters got a clue what's going on?