Mixing Dry Malt and Dextrose in water and get to temp days before fermentation?

[DAN831]

So I mix the Dry Malt and Dextrose with boiling water and pour it straight into a sterilized Juice Bottle with good sealing lid and put in STC controlled brew fridge that has my 2 fermenters with the water needed inside for the extract kit im about to mix and add yeast, i leave this for sometimes a few days before mixing. the point is to get all ingredients down to 18 degrees before i want to mix together and add the yeast.

question is can I store that Light Dry Malt and Dextrose mix in the bottle at 18 degrees without infection or is it a pure disaster waiting to happen?