The “two-minute rule” has two parts.
First, if something takes less than two minutes, do it now. Next, start building new habits for two minutes at a time. The rule for this is: When you start a new habit, it should take less than two minutes to do. The idea is to make your habits as easy to start as possible.
Think of these “two-minute habits” as gateway habits that will lead to your overarching goal.