Your Project Timezone is reflected on Graphs as well. End of a workday is calculated according to your project timezone. Graphs retrieving data on date-field values may show you time information differently if local timezone is not same as your project time belt. Project Admin can edit your Timezone values in Project Settings. Logout once to reflect new time zone settings. Change in Time zone will reflect only in later item updates.
Note: Contact your admin to access “Project Settings”