When it comes to smelling a violet, then you have to be fast or else you are going to miss out. That is not because the scent only survives for a few seconds as it is always there, but it is where the scent comes from and the impact that it has on us that makes the difference.
It turns out that the scent from this particular flower comes from iodine, and this is something that our brain is not too friendly with if truth be told. The impact that it has on our scent receptors is that it shuts them off after a short period of time, so we are then unable to smell the flowers in the same way. To us, it is as if the scent has died, but it is still there. If you step back, wait a short while and then smell them again, then it will suddenly work with the entire process being repeated.