1) Reciting the Quran to perform Isal e Sawab for a deceased person is permissible at any time, whether at their burial site or elsewhere. However, there is no evidence from the Noble Hadith to support the practice of reciting a specific surah at the burial site of a deceased person for forty days.
2) It is mustahabb to recite the first 5 verses of Surah Al Baqarah while standing near the head of the deceased, and the last two verses of Surah Al Baqarah while standing near their feet, after burial. Similarly, the Noble Hadith mentions staying at the grave for a short while after burial to pray for the forgiveness and steadfastness of the deceased.
Note: The phrase "stay for a while" in the hadith refers to the amount of time it takes to slaughter a camel and distribute its meat, as explained by Hazrat Amr bin al A'as (ma Allah be pleased with him). It is important to note that this does not mean that a camel must actually be slaughtered and its meat distributed. Rather, it is simply a way of measuring time. The Arabs were known for their efficiency in slaughtering and distributing camels, so this was a common reference point for them.
For more details, please refer to fatwa number 5509.