If I have the double gene mutation (homozygous) for hemochromatosis but am not clinically iron overloaded (have high iron levels on lab results) at this time, can I develop iron overload later, such as in 2, 5, or 10 or more years later?

Hemachromatosis. The single gene carrier will likely not develop any symptoms or problems from increased iron absorption. You will still need to have regular blood work to check for increased iron, and not use any supplements with iron. If you have two genes, your chance is good that you will have high levels of iron, and possibly get damage from the extra iron. Timing is unknown, too many variables.
Yes. The onset varies based on other factors, especially sex. Females are relatively protected until the menopause due to monthly blood loss. Other factors can also be managed. Talk to your doc.