Step 1: Think of PPCM as a pregnancy-linked dilated cardiomyopathy. The defining feature is the timing of onset, not the symptom set, which simply mirrors any heart failure.
Step 2: The accepted diagnostic window runs from the final weeks before birth to roughly $5$ months after birth. A new-onset cardiomyopathy outside this window is, by definition, not labelled peripartum.
Step 3: Mapping the choices to this window: $7$ days and $6$ weeks cut the window short and exclude valid late cases; $24$ months stretches it so far that other dilated cardiomyopathies would be misclassified. The five-month limit fits the definition exactly.
\[\boxed{\text{Within 5 months}}\]