Section 6166(k)(3) provides:

(3) Period of limitation

For extension of the period of limitation in the case of an extension under this section, see section 6503(d).

Section 6503(d) provides:

(d) Extensions of time for payment of estate tax

The running of the period of limitation for collection of any tax imposed by chapter 11 shall be suspended for the period of any extension of time for payment granted under the provisions of section 6161(a)(2) or (b)(2) or under the provisions of section 6163 or 6166.

Sections 6161(a)(1) and 6161(a)(2) provide:

§6161. Extension of time for paying tax

(a) Amount determined by taxpayer on return

(1) General rule

The Secretary, except as otherwise provided in this title, may extend the time for payment of the amount of the tax shown, or required to be shown, on any return or declaration required under authority of this title (or any installment thereof), for a reasonable period not to exceed 6 months (12 months in the case of estate tax) from the date fixed for payment thereof. Such extension may exceed 6 months in the case of a taxpayer who is abroad.

(2) Estate tax

The Secretary may, for reasonable cause, extend the time for payment of-

(A) any part of the amount determined by the executor as the tax imposed by chapter 11, or

(B) any part of any installment under section 6166 (including any part of a deficiency prorated to any installment under such section).

for a reasonable period not in excess of 10 years from the date prescribed by section 6151(a) for payment of the tax (or, in the case of an amount referred to in subparagraph (B), if later, not beyond the date which is 12 months after the due date for the last installment).

Section 6163 provides:

§6163. Extension of time for payment of estate tax on value of reversionary or remainder interest in property

(a) Extension permitted

If the value of a reversionary or remainder interest in property is included under chapter 11 in the value of the gross estate, the payment of the part of the tax under chapter 11 attributable to such interest may, at the election of the executor, be postponed until 6 months after the termination of the precedent interest or interests in the property, under such regulations as the Secretary may prescribe.

(b) Extension for reasonable cause

At the expiration of the period of postponement provided for in subsection (a), the Secretary may, for reasonable cause, extend the time for payment for a reasonable period or periods not in excess of 3 years from the expiration of the period of postponement provided in subsection (a).

(c) Cross reference

For authority of the Secretary to require security in the case of an extension under this section, see section 6165.

Section 6165 provides:

§6165. Bonds where time to pay tax or deficiency has been extended

In the event the Secretary grants any extension of time within which to pay any tax or any deficiency therein, the Secretary may require the taxpayer to furnish a bond in such amount (not exceeding double the amount with respect to which the extension is granted) conditioned upon the payment of the amount extended in accordance with the terms of such extension.