Ideally after the funds are committed but before the investor needs to be on site working, using an escrow that closes on visa issuance. Book the consular interview as soon as the escrow is funded and the file is complete, and build the planting season around the visa date rather than the reverse.
Fund the escrow, interview, then close and plant
Hypothetical example: a Haldimand County greenhouse grower must take over a U.S. nursery before spring shipments arrive, but does not want to own a business she cannot legally run. The workable sequence is an escrow agreement in which her purchase funds are deposited and released to the seller when the E-2 visa is issued, with return to her only if it is refused.
That shows irrevocable commitment while protecting her. She then applies at the consulate with the full file. Consular appointment availability varies, so request the interview the day the escrow is funded and the business plan is finished.
Until the visa is issued she can visit the nursery as a business visitor to inspect and negotiate but cannot manage staff or handle sales. If the seller will not wait, the fallback is closing first and applying immediately afterwards, accepting that she owns a business she cannot operate in person until the visa is granted. Decide which risk the household prefers before signing the purchase agreement.