Is visiting one's deceased father in the graveyard considered a form of dutifulness that benefits the visiting son, and is it comparable to visiting him during his lifetime, and what is the maximum period for the interruption of such visits?

Visiting graves is commendable for reflection and remembering the Hereafter, and to benefit the deceased by supplicating for them and seeking forgiveness. However, visiting one's father after his death is not obligatory. Righteousness towards him is achieved by supplicating for him from anywhere, and supplication reaches the deceased without a visit. Sheikh Ibn Uthaymeen (may Allah have mercy on him) was asked about visiting the deceased, and he replied that the purpose is to supplicate for them, and this reaches them wherever the supplicant may be, with no need to undertake a journey to their graves. If the grave is in the same country as the visitor, there is no harm in visiting it. There is no specific time limit for visiting one's father after his death; he can be visited every Friday or more or less frequently.