A short gratitude meditation asks little more than a few quiet minutes and a willingness to bring specific things to mind: a person, a comfort, an ability, something ordinary that would genuinely be missed if it were suddenly gone, held in attention for a moment rather than rushed past.
The brevity is part of the appeal, since a two or three minute practice fits far more easily into a genuinely busy day than a longer, more elaborate session, which makes it considerably more likely to actually happen consistently rather than being postponed indefinitely in favour of something more urgent.
Even this short a practice, repeated over weeks, appears to shift a person's general disposition slightly, making a grateful noticing somewhat more available by default during the rest of the day, not only during the few minutes deliberately set aside for the meditation itself. That quiet carryover, from a few deliberate minutes into the rest of an otherwise ordinary day, is arguably the whole point of the practice.