All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad
is His slave and Messenger.
From what we understood from the question, you are selling these services to businesses. If that is the case, then there is no harm in selling such services for whatever price you mutually agree upon, even if you calculate the price based on the total number of hours, as long as there is no lying or deception. Thus, do not say, that you purchased all the hours, when you actually acquired some of them for free.
It is mentioned in an authentic hadith regarding buyers and sellers: “If they speak the truth and make clear [the defects of the goods], their transaction will be blessed for them. However, if they lie and hide [some facts], their transaction would be deprived of Allah's blessings”.
Allah knows best.