Is it a digit haiku?
Retina 0.8.2, 25 bytes
0|7
_#
^.{5}\w.{6}\w.{4}$

Try it online! Link includes test cases. Explanation:
0|7
_#

Expand 0 and 7 into two syllables.
^.{5}\w.{6}\w.{4}$

Check that neither the 6th nor the 13th syllable is the second such syllable.