Starting Up a 401k Plan After Terminating a DB Plan

A company that only employs the owner sponsors a DB plan and wants to terminate it and start up a new 401k plan because the DB is getting very close to becoming overfunded.  Perhaps I'm confusing two different topics, but I seem to recall that there's a rule where you have to wait at least one year in some instances before you can start up another plan.  I believe the purpose of the rule was to prevent an owner from effectively taking an inservice distribution prior to age 62 (i.e., the distribution resulting from the DB terminating) while continuing to accrue additional benefits via a new 401k plan.  I've found references to sponsors terminating DB plans and immediately starting up 401ks without such an issue mentioned, so my question is under what circumstances do you have to wait a year before starting up a new plan?  TIA