PEXA transfer of funds

Hi all, while i wait to hear back from my conveyancer.. is anyone able to tell me if a shortfall amount is transferred to PEXA the morning/time of settlement out of a nominated account or do PEXA take a hold on the amount days prior?

My conveyancer has advised the funds will debit from my nominated account but to ensure they are there 3 days prior.. I wasn’t sure if this was a PEXA requirement or my conveyancer ensuring the money is there and ready to go.