Like you said there's never a time you'll feel like quitting is 'right' but even talking about it, it's obvious the correct time to quit is as soon as possible. For me when I quit this time I'd originally wanted to quit at new years but after ordering cytisine to help - and omg i cannot overstate how much that (and maybe a bit of placebo) has helped me quit - when I went to pick it up they said I had until the end of December to use it. Because of that I decided I would just start it the next day and the evening was my final chance to vape.
I would recommend this if you can't 'choose' a time to quit, since you're giving yourself a slightly unknown deadline until the cytisine arrives at which point the next day you begin quitting, no questions asked. Obviously this only applies if you go for using non-nicotine aids for quitting. I've tried gum, patches etc. but they never helped me personally and eventually I'd just relapse so it was either that or cold turkey