Hi Larisa, I have the same issue. Sometimes when I practice, it's hard to tell what I'm actually looking it. Today I just looked at my hand for a moment and I was already seeing some glowing around the edges. I don't think that you can get an afterimage in under a second as a result of practice.
My advice to you is to just keep practicing and don't get discouraged. I still have a long way to go but I can tell you that practice has improved my consistency. I can now tell you that I'm likely to see a certain amount of "sparklies" (which can't be afterimages because I wasn't seeing anything there before) every day and I'm guaranteed to see the glow at the edges of everything I can see. You can always alter your practice later, but don't let your uncertainty deter you.