Hi Braincleaned,
I was never disfellowshipped, but after 2 1/2 years aftering leaving the faith, I was subjected to disassocation by action. This was in response to my decision to openly celebrate Christmas including putting lights on my house. As far as I am aware, there is no specific time limit after leaving wherein the elders feel that cannot act, although there is some guidance for elders in their elders-only policy manual about whether or not the individual views themselves under the authority of the congregation. In the case of disassociation by action, the decision is entirely internal to the elders and the person who is the subject of the announcement may not even be informed, or if they are, it is viewed as a "courtesy."
Sad to say, the faith concerns itself with indications of control and obedience by members and former members alike. Open displays of disobedience, even by long-time former members, can be met with reprisal.
Cheers,
-Randy