I'm pretty sure I have an umbilical hernia. If I were to have surgery how long should I expect to be off work?

About 5-7 days. The time off of work is less if the hernia (and incision) are small. You shouldn't drive while you are taking narcotic pain pills. You could go back to work with no heavy lifting in less than a week if the hernia is small. The surgeon will probably recommend no heavy lifting for about 4 weeks.
Variable. It depends on the size of the hernia, your medical condition, and the technique of repair and the type of work you do. The typical range is 1 day to 2 weeks for small hernias performed as an outpatient. You should see a general surgeon for a consultation regarding your unique situation.
About a week. After an umbilical hernia repair, generally you should expect to be off work a week. After which you can return with lifting restrictions for about a month.