will HQ dissolve at room temp...

[Wayne]

...In a developer stock solution that is already mixed?

 

[eumenius]

Usually that's not a problem - Metol won't dissolve well in strong sulfite solutions, and HQ should dissolve well if the alkalinity is right (and it's right if the developer is already mixed). If it won't dissolve well, what I doubt, you may try to re-heat a bit the whole developer in microwave oven (30-40 Celsius), taking care not to aerate during stirring the warm developer too much, to prevent it from possible oxidation.