ido-enter-matching-directory

ido-enter-matching-directory is a variable defined in `ido.el'.
Its value is

only

Documentation:
Additional methods to enter sub-directory of first/only matching item.
If value is 'first, enter first matching sub-directory when typing a slash.
If value is 'only, typing a slash only enters the sub-directory if it is
the only matching item.
If value is t, automatically enter a sub-directory when it is the only
matching item, even without typing a slash.

You can customize this variable.