If this is your first 401(k) plan for your business, your Safe Harbor plan is required to be set up three months prior to the plan year-end date. So if your business is on a calendar, fiscal year your plan must be established by October 1st. It typically takes 1-2 weeks from the purchase date to complete the installation of your plan. Note that traditional and Solo 401(k) plans have different deadlines that are much closer to the end of a fiscal year. If you have an existing plan, you may start the transfer process at pretty much anytime.