Which sentence is Punctuated correctly?

• The conference was only supposed to be an hour; however, it ran for nearly two and half hours.
• The conference was only supposed to be an hour, however; it ran for nearly two and half hours.
• The conference was only supposed to be an hour. however, it ran for nearly two and half hours.
• The conference was only supposed to be an hour; however it ran for nearly two and half hours.