How long to wait for non-responders?

[AlbanyConsultant]

What kind of time frame do you usually allow to go through the FAB 2004-02 steps during a plan termination?

Let's say the initial forms go out certified mail, so that doesn't have to be repeated. And the plan sponsor also attempts to contact the participants using beneficiaries to no avail. What's a "reasonable" time before sending something to the IRS or SSA letter-forwarding services? And, more importantly, what's "reasonable" before just sending the money to a Penchecks or Millennium Trust or someplace like that? I would think you'd want to have that decided up-front so you can put it in the initial letter: "If you don't respond by X, your money will be sent to Y."

Thanks!