Early enough that access, permissions and spending are demonstrable, but not so early that you pay for months of unused capacity. There is no universal rule requiring a signed lease before filing or forbidding one; counsel should reconcile the agreement's start date, termination rights and your production plan against the evidence the case needs.
Sequence commitments so the case shows a live operation
Build the launch calendar around milestones you control — agreement executed, permissions filed, equipment ordered, first production run scheduled — because no processing time, appointment date or outcome can be guaranteed. A hypothetical owner might keep several months of operating reserve so an unopened kitchen does not drain the enterprise; that is planning, not a legal requirement. Remember that visa validity and the authorized stay on your I-94 are different periods.
Useful milestones include the executor's confirmation of the next distribution, the transfer of committed funds, the signing of the lease or purchase, and the completion of the source and path record. The purchase agreement should therefore be signed, the price deposited with an escrow agent, and the closing conditioned on visa approval, with the money returned only if the visa is refused.
Fix dates for the entry list, the supporting documents, the signed memo, any amended filing, and counsel's review of the final set.