The Commissioner of Social Security shall prescribe the period or periods of time within which, and the manner in which, various kinds of property must be disposed of in order not to be included in determining an individual’s eligibility for benefits. Any portion of the individual’s benefits paid for any such period shall be conditioned upon such disposal; and any benefits so paid shall (at the time of the disposal) be considered overpayments to the extent they would not have been paid had the disposal occurred at the beginning of the period for which such benefits were paid.