I see your point PK, it would definitely make sense. But there's a lot of situations in the movie where you can't really tell how much time has passed between one scene and the other.
As the others have said, your thread is quite interesting. I have always imagined it was the next day; Scar didn't need a lot of time to make his brilliant scheme to kill Mufasa and Simba. If you listen to Be Prepared, it seems as though he had a plan by the way of his knowing. He wouldn't have told all the hyenas by yelling and with an evil smirk; he must have had a plan thought up by then. Okay, maybe he would have, but the point is that I believe he had a plan by that time.
Either that or he could have been spontaneous and thought it up as he did it.
'Cause you're beautiful. Like no other. Flawless, absolutely flawless. <3