Gmail calendar sych works via exchange/push somehow. You must have push enabled, push is quick but it isn't instant. Push is designed to not use a lot of battery, somehow a push server reaches out to your phone only when it has something for you. Seems to be some sort of direct contact service, I know hactivated phones on something like tmobile have to have a pushfix workaround. Seems like a component of hactivation gives you a non unique push identifier so it can't sort you from the crowd of other hactivation users. Reading up on that could give you an idea on how push services work.
I have the gmail account set up as exchange and it is set to sync mail and calendars under the exchange account, I left out contacts. Events appear on the phone without any action taken, notifications happen on my phone for new events on my gmail calendar even if I never opened the calendar on the phone. Then on my work PC I have gmail calendar sync running to push/pull events from my outlook calendar to/from gmail calendar. That is a synch every 15 minutes or on demand. Whole thing works really well for me.