Dark room veg cycle ?

ok so im thinking about doing a dark room to double my yeild i understand the concept and how it works for the most part, now what i need help with is when the plants are in the veg cycle with 18:6 how does it work do i add a light to my dark room so after the 6 hours they get 12 hours and then switch the one in the light in to the dark room ? is their a another time i can use for veg?with the flowering its 12:12 so the plants will be switched at the same time so its simple sooo where im at now is how it works on the veg stage please reply i looked on google but got no where,
thank you for the help

yes lol if i have 1 light room and 1 dark room. for the seedlings they all will be in the light room. when i switch to veg half the plants go into the dark room on a opposite time schedule. so if the ligts are on for 18 hours the other plants only need 6 hours of dark when it comes time the lights room isent ready to be switched out. in the flowering its 12/12 so when the light room needs dark, the dark room needs light. do you understande my confussion

You only need one veg room and one flower room. If you only have one room, you could veg your plants out, and turn down the lights to 12/12 after your veg plants are ready to flower.

You don't move your plants from room to room put the lights on timers 12/12 in one room and 18/6 in the other your vegging plants stay in one room until they are ready to flower and your flowering plants stay in one room until they are done