26 CFR §1.6164-4

1. (a)Time for payment. If an extension of time relates to only part of the tax, the time for payment of the remainder of the tax shall be considered to be the dates on which payments would have been required if such remainder had been the tax and the taxpayer had elected to pay the tax in installments as provided in section 6152(a).
2. (b)Example. The provisions of this section may be illustrated by the following example: