In Canada, we do start wearing poppies about November 1st and wear them through November 11. It used to be that you would wear them all day on the 11th but it has become tradition for those attending cenotaph services to leave them there as they left so others who do not attend services remove their poppies around noon.
The biggest culprit in stripping you of your poppy is the danged seatbelt. I've started putting a little bit of clear tape around the end of the pin, after I've woven it through, which seems to work. I'd read that using a flag pin to hold the poppy on was not to be done but after seeing a number of older veterens doing this, I think it is OK. Afterall, they are some of the ones we are honouring so if it is OK with them...
It is also appropriate to wear a poppy on other occasions that are honoring war dead, such as D-day anniversary memorials.