Petty Cash Expenses in Construction c+ contract should be recorded as cost at the time of payment or at time of receiving the supporting documents?

at the time receiving of supporting doument

At time of payment it is treated as advance payment, at the time of receiving the supporting document cost has been charged to project.

COST RECORDED AT TIME OF RECEIVING THE SUPPORTING DOCUMENTS. 

recorded at the time of receiving supporting documents.

Petty cash cost recorded at time of receiving the supporting documents