思い立ったが吉日
also: おもいたったがきちにち
Meanings
1
there's no time like the present; act on an idea right away
Proverb encouraging immediate action when inspiration strikes; literally 'the day you think of it is an auspicious day.'
If you feel like traveling, there's no time like the present—let's start planning right away.
They say there's no time like the present, so I decided to start a new hobby today.