when to switch from mh to hps and veg to flower nutes

so I have always switched as soon as I switch to 12/12. is this correct or should I be switching light after I see preflowers.

Same with nute I switch to flower nutes when I 12/12. should I use veg nutes until preflowers +rep for input

what i do (just saying) as soon as i switch the hours i change the lights and i also change the nuts...my reasoning for doing the nuts immidiately is that i usually grow in soil so it will take a little bit to get the veg nuts out of the dirt. plus i believe the boost in phosphorus helps initiate the bloom cycle (this is just my opion its not based on fact, but thats the way i grow). if you are doing hydro i don't want to give any advise because i only have 4 grows under my belt on that...im not a big fan of growing hydro i like the traditional method better.

When you flip your lights flush your plants or change your nute tank. Stop w/ the N in the NPK cycle of life and grow on withy our bad self.

Gotta see that papaya!