You may find that your ical invites or other timestamps on your Moodle site are not correct. If this is happening you can quickly check the settings and update them if applicable.
In order to change your timezone for your site go to Site Administration > Location > Location Settings
From this page you will see your location settings, users can often have their timezones different to the default, for organisations operating exclusively in the United Kingdom you can Force a timezone which resolves most issues.
If you operate in multiple timezones ensure the default setting is Users can choose their own timezone and ensure on each learning account that they have the correct setting selected.