Change the interval for "hard" answer

You can do even better; there is add-on “Rememorize…” which lets you have ANY interval you want; just click ‘m’ and input the number; ‘Return’ will accept your input. And (!) the Ease will not be decreased.

The add-on has a few options but you want the ‘Reschedule’ one; to make it even more efficient, you can change the default input.

When the card comes back for the next review, you can

  1. Accept the Anki interval or
  2. Reschedule the card as far to the future as you want.

Related:
Another add-on has 1d interval option; it is [Slackers’ Delight (Postpone/Defer Button)]; but 1d ivl is too small – in this case, IMO.
But it is nice to have 1d ivl available at any time - with One click.