There's no single right answer to how often an office should be cleaned, but there is a right way to figure it out. Start with how many people use the space each day, then look at the areas that get dirty fastest: restrooms, break rooms, and the walkways from the front door to the desks.
Offices with more than about twenty people on site most days usually need restrooms, kitchens, and trash handled daily. Desks and low-traffic rooms can often go to two or three visits a week without anyone noticing a difference.
Floors set their own schedule. Carpet in the main traffic lanes benefits from vacuuming every visit and hot-water extraction a few times a year. Hard floors in entries and break rooms need regular mopping plus periodic scrubbing and recoating to keep their finish.
The best approach is a written scope that splits tasks by frequency: what happens every visit, what happens weekly, and what happens monthly or quarterly. That way you pay for what the space actually needs, and nothing quietly drops off the list.