How to "synchronize now" the ipod touch with google calendar?
It's possible that, for some reason, push can't go through. In those situations, your iPhone will fall back on the fetch schedule. Go to Settings->Mail, Contacts, Calendars->Fetch New Data and make sure that you select the most frequent Fetch, which is 15 minutes. It's certainly a far cry from the instantaneity of push, but you shouldn't have to wait more than 15 minutes for stuff to come through.

Also, you should check under Advanced just in case your schedule for your Google account was changed for some reason - it should be "Push".