transition period; period of transition
Used for a defined period during which a system, rule, or organization changes from one state to another. Common in business, IT, and legal contexts.
We plan a three-month transition period to the new system.
During the transition period, the old system will also be used.
移行期間 refers to a set, often officially scheduled transition period, while 過渡期 stresses the unsettled, evolving nature of the change itself.
Compound of 移行 (transition) and 期間 (period).