Doubt you would spend a day at immigration.
If you do, you might do something wrong or do not have the required information at hand.
After few years you should know what is required for an extension each year.
I spent 30 to 45 minutes at the immigration office to get the yearly extension.
Total travel time, to and from the immigration office, 30 minutes.
Once a year, free of charge.
The beauty of not using an agent.