Hey,
just to say, i think ,suggest, you should apply the powder now, or sooner. I have used the piranha powder, and that too is 'meant' to be used the first two weeks of flower. I would say to get any benefit from these products(beneficial fungi)they should be used in veg(with such a short time crop, like pot)and if in soil, or coco you could probably be only apply them once or twice and colonisation would occur. Or they should be reapplied if your using very acidic ferts for example. Or in hydro...
But yes you could use both the products at the same time, as they would be preforming two different functions.
I guess the other thing would be what your stimulator is, and if it has a nutritional value, which could effect the colonisation of the roots.
Personally, after using piranha, the only thing i found was a dramatic water usage drop. This was The only indication i had of root colonisation. I dont have a lab to analyse the roots after to check, so could of been something else.
But what i was trying to get to was that i think these fungi/bacteria need to be applied earlier than stated to get any benefit. Also that alot of the fungi actually rob the plant of carbohydrates, which ,from what i understand, are important for bud building. So i wont be using them in flower again. Thats just me though, i say try it with and with out and make your own choice on its effectiveness.
So yeah,depending on how and what your stimulator is will effect how you apply it, and therefore, how it will affect your microbes.
Take it easy., and best of luck.