Hi @Pau_Josa 
After the first sync with Google Calendar, it will take up to 24 hours for a refresh and for any additional task information to appear. After this, it is up to Google’s software as to how often it updates the calendar.
While we can’t influence how many time Google performs syncs with Asana, we have reached out to Google’s engineers and have submitted a feature request to increase the frequency in which their calendars update. However, they were non-committal as to when or if they will implement this new functionality to Google Calendars.
Hope this answers your question; please let me know if you have any follow-up questions!