As with most things on the website, the events system is set to work from the timezone you set in your user settings. Unfortunately, due to the wide range of timezones that TAW members are a part of, these settings can have some adverse consequences.
For example: You have created an event in your local time, which is 19:00 GMT. Another officer in your unit has then edited the event, but they are in a different timezone, CET (GMT +1). By saving the changes and not adjusting the time in the event to the time that it should start, they save the event with the 19:00 start still set. Due to this setting, this will change the event to 19:00 CET and as a result will show an hour earlier for anyone in GMT.
We understand that this is not an ideal scenario and will look into solutions. Until then, if events are appearing a few hours out of sync, try editing it and resetting the start time to the time it begins in your local timezone.