Damnant quod non intellegunt. They condemn what they don’t understand. (used to explain why someone might foolishly disagree with a good plan)
Dictum ac factum! No sooner said than done! (used to show that a person is ready to follow instructions quickly and without complaining)
tempus fugit time flies (used in the same way as the English phrase)
ipso facto by the fact itself (used as a very strong form of “therefore”: therefore, as an inevitable result…)