Once you give the person the +karma it shows instantly. Yes once you give one karma you can't give to that user again till 10 hours.
My bad, I did not realize that, even though I noticed 2 times that I gave karma to 2 members but it was not added to their profiles, I thought there must be some delay in the addition of karma so I never double checked, I guess I should find those posts again to give them karma, especially the ones where I write +1. I doubt if my karma to such posts was added or not. But now I think there is no way to confirm that either.
Because I not even remember how much karma they had when I give +1, I actually write 3 to 5 times +1 in my posts in response to some member's post and gave them instantly after making the post, but never checked, well, that's bad for me. Thanks for the confirmation dear agbe, from now on I will be more careful.