This issue happens when the timezone on your Appointy and Google calendar is different. Please make sure that the timezone is SAME in both the calendars. Here's how to troubleshoot:
1. Appointy: Go to SETTINGS ~~>> BUSINESS DETAILS ~~>> Timezone and Currency section of Appointy admin
2. Google Calendar: You can set it from Settings link (see the screenshot attached)
If still you have problems then feel free to contact us at firstname.lastname@example.org. OR you can schedule a convenient time from http://support.appointy.com for a guided screen sharing session with our support staff. We will be happy to address your issues and concerns.
Note: Once you change the timezones, all your appointments (after the changes made) will be under effect of new timezones