ars = art, skill, method, science, technique, craft, conduct
et = and
ratio = system, manner, method, procedure, theory, reason, judgement, consideration
revocandi = to call back, recover, refer, revoke
temporis = of time, short-lived or temporary
praeteriti = past, expressing or describing a past action or condition
Heh, my translation - "The art and system to recover a lost/previous time"