Microsoft Office 2010 needs to be activated after 30 days. It can be rearmed 5 times, every rearm gives you additionally 30 days to activate.
If you always rearm it on the last day before it has to be activated that makes a total evaluation time of 6 * 30 = 180 days.
Although the rearm feature was made for corporate users, it cannot be illegal to use it since it's an official feature.
You can use this tool to rearm Office 2010 5 times. Just re-apply once the 30 days are over.