Must the vision from Istikhara in a dream occur immediately after performing Istikhara?

We do not have knowledge of dream interpretation and apologize for interpreting what you saw in your dream. A good dream after performing Istikhara can bring optimism and comfort, but it does not necessarily indicate something related to the matter for which Istikhara was performed. If it becomes clear to you that the suitor is a man of religion and good character, then proceed with marrying him as long as you have sought guidance from your Lord, and goodness lies in what Allah decrees.