Mixing hydro nutrients before adding to res

I use Humboldt Oneness, Ginormous, Sea Cal and Sea Mag as part of a regular schedule. I have now gotten conflicting answers from Humboldt on whether it is ok to mix the four together in a quart or so of water before adding to each of my four reservoirs. The alternative is measuring each of the four and adding to each of the reservoirs, a 16 step process. I don't see any reason for this. I see nothing about the interactivity of any of the components that make it a problem to mix them in a quart of water since they are soon going to be mixed anyway, albeit in a lower concentration.

Wondering how other hydro growers do it.

I mix my stuff in a gallon of water then add it to the rez.

i have 50gal res's and it take me less than 12mins to drain, rinse, fill, add nutes and additives, and adjust ph. i have up to 7 items to add to each.

I add RO water to my bucket, then add the nutrients per N level or additive directive. Then just swap out to desired plant, never timed how long never thought I need too...