For DIBS project, the developer will absorb the intetest during construction period. So there is no point of putting the money to reduce loan interest during construction stage as in the first place the interest is born by developer. The money that you dump in serve no purpose and very likely won't earn you any interest (even there is, it will be pathetic)

After completion / VP, you may dump in more than the required scheduled instalment to reduce the interest. If it's full flexy then you will be able take back your extra payment anytime from your current account. If it's semi flexy then you will have to write in to request take the extra money.