English to Japanese Bus/Financial Law: Contract(s)

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Time Schedule and Scope of Supply: X + 3 month; Circuit Diagrams
X is defined as date of contract signing furthermore until the down payment is received.
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Is X the time when contract is signed, or is it when the down payment is received, or
is it when both are done? Or is it that X is temporarily set as date when contract is signed
and is going to change when the down payment is received?