Do the dead recognize their visitors, return their greetings, and hear them, and do they feel the passage of time between one visit and another? What are the recommended days for visiting graves, and what is the interpretation of Allah’s saying: "It will be as though they had not remained [in the world] except for an afternoon or a morning thereof"?

The meaning of the verse is that when the dead witness the Hour of Judgment, they will feel as if they had not lingered in their graves for more than a very short period, like an evening or a morning. This is to minimize the duration of worldly life. A Muslim must prepare for the life of the Barzakh (interim period between death and resurrection) to be among the felicitous therein.