Generally it involves at least 6 months where the parent has had no contact whatsoever. Paying child support is considered contact, and obviously so is visitation/calling/emailing/letters etc.

In most cases though, it would be at least a year to be on the safe side.

Quite often in a Step-parent Adoption situation, the absent parent may be given at least once chance to remedy the absence before their rights are involuntarily terminated.

A good attorney however may be able to avoid this from happening.