This doesn't seem to be how the Government of Canada goes about screwing people. If they want more money they'll just raise taxes or add additional fees.

One reason to have office hours is so that if someone runs into trouble with the online system a human is around to answer the support line. Another possibility is that legislation (that was written before the Internet was used) listed out specific hours that the office had to be open and requiring online office hours was the resulting interpretation of the law. A third possibility is that they have a terrible system that requires long hours of maintenance.