I agree with [...]. We have no 'hard' evidence that this mixture is a true solution (i.e. each and every molecule of lorazepam in the tablet goes into solution when vodka is added and stays in solution when more water is added).
Consequently, to be on the safe side, might I encourage you to treat your homebrew liquid as a suspension not a solution? Shake it vigorously before you use it and measure your reduction as quickly as possible. Members who’ve had success with this type of homebrew liquid seem to follow both of these practices.