Praise be to Allah.
If the Muslim is not able to visit the graves except on Fridays because he is working on all other days of the week apart from Friday, then it seems that there is nothing wrong with that because by doing that he is not singling out Friday as having an advantage over other days. He is not doing that because he singling out Friday for that purpose; rather it is because it is his day off.
Shaykh Ibn Jibreen (may Allah have mercy on him) was asked: Friday is a day off for us; if we single out this day or a few hours of it for visiting graveyards, does this come under the heading of bid‘ah (innovation)?
He replied: It does not come under that heading, because there were some reports which speak of visiting graveyards on Friday. … So long as you did not deliberately single out this day and this is when you have free time, then there is no sin on you in sha Allah. There are some reports that speak of singling out this day and of its virtue, but they are not proven. End quote from Fataawa Ibn Jibreen.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: The apparent meaning of the evidence indicates that it is general in application and that it is makrooh to single it [i.e. Friday] out for fasting, whether it is an obligatory fast or a naafil one. But if a person has work and is not free and he cannot make up his fasts except on Fridays, then in that case it is not makrooh for him to single out this day for fasting, because he needs to do that. End quote from Majmoo‘ al-Fataawa, 20/55
And Allah knows best.