The office is open from 7am-7pm, Monday-Friday. Some employees may have access to the office outside of this window, but it's only for extreme circumstances (like software failure that needs immediate attention). Most employees, unless otherwise discussed, have a certain degree of discretion over the hours they work. To ensure there is ample overlapping time for teammates to work together, the hours you choose should include the hours of 10am-4pm (with the exception of a reasonable lunch break).
For example, let's say you're expected to work 40 hours per week, the equivalent of 8 hours per day. If you're a morning person, you may want to work from 7am-4pm with a one-hour lunch break. If you really dislike mornings, 10am-7pm might be more desirable. Most employees fall somewhere in-between.