Translation of "whenever" into Latin

It was the rule of our ancestors that, whenever there was first an offence, some penalty should follow.

minui iura quotiens gliscat potestas, nec utendum imperio ubi legibus agi possit.

Whenever you warn someone, and he does not wish to be warned, do not stop once you have begun if he is dear to you.

Cumque mones aliquem, nec se velit ille moneri, si tibi sit carus, noli desistere coeptis.