Early enough that the gift is complete, traced and invested or actively being invested before the petition is filed, because capital is tested at filing. The two-year conditional period starts later, on admission as a conditional resident.
The gift precedes the investment, and the investment precedes the petition
The order is fixed by the rule that capital must be invested or in the process of being invested when the petition is filed. The parents' sale must close and the proceeds settle; the gift deed is signed and the funds move to the investor's account; the investor commits them to the enterprise or its escrow; and only then is the petition filed with the complete trace. Compressing these steps invites gaps in the bank records that are hard to explain later.
The second clock, the two-year conditional residence, starts when the investor is admitted or adjusted as a conditional permanent resident after approval and visa availability, and the I-829 window opens ninety days before the second anniversary. Between the two, the investment must be sustained and the jobs created, so the project's timeline should be read against expected processing. Do not let a project's subscription deadline push the family to file before the parents' records are complete.