hardly / scarcely
Two adverbs that already carry a negative.
Hardly and scarcely already lean negative. Do not add not: not can’t hardly. The pair with when is hardly … when or scarcely … when, not than. Barely follows the same pattern.
Examples
UseShe hardly had time.
UseHe had scarcely sat down when the phone rang.
AvoidShe can’t hardly see.
AvoidHe had scarcely sat down than the phone rang.