I'm going to assume this is a serious post and not simply trolling. I think timming depends on what your after. I often mix base in with my toner a level below what i achieved with lightener. This allows me to process the tint longer. I find when i do this the results are more long lasting and more natural. The down side is that I don't achieve the brightness and shear results that many bleach and tone clients are looking for. For successful toning two thing are crucial. Knowing the level and being honest with yourself about what you have achieved, and secondly, knowing what tones need to be neutralized in order to achieve the desired results.
Im just curious alot of ranges have specific toners. Mine say 15min to 25max. Ive never had the grey issue. Saying that though I always do what they say though about porosity filler and gold parts first that i want to tone most then apply to rest of hair with the same mix +clear