I do not have the knowledge to answer your questions... maybe someone like Lapis could help with these?
That said, I will try.
I do believe that the clay can and does act as a detox of sorts by itself. Whether it would improve the efficacy of the heavy metal detox or muddle it up, I do not know.
When eating out it is hard to avoid microwaved anything if it is cooked food and served hot. This is unfortunate as it renders the nutrition in the food unrecognizable by the body, it also destroys what little life giving structure there is to water.
If it where me, I would probably wait at least two hours and take the clay after the meal on an empty stomach.