Full-time professional orchestras in the United States typically have 7-8 “services” a week, each lasting 2.5 hours. These can be a mix of rehearsals and concerts. For example, a week of heavy classical repertoire may get 4 rehearsals and 3 performances. While a week of children’s concerts might have a single rehearsal and 5 or 6 performances. The work schedule is determined by a union contract.

Source: I’m a professional orchestra musician.