You can manage as few or as many as you have in your organisation. We have many companies with only a handful of staff, and at the other end we have companies with hundreds of staff.
With Timetastic you can group your staff in departments, just like your organisation's internal structure. With this you are effectively splitting down Timetastic into smaller chunks that can be managed by departmental bosses, and you should find no limits to the number of employees you can put on the system.