The preposition intrā takes an accusative. It is likely derived from the adjectival feminine adjective singular of inter, intra, intrum (intrā) — an archaic adjective which also produced the corresponding preposition inter.
Intra + accusative is primarily used with a single class of nouns, and denotes a space ‘within which.’
intrā moenia, within the walls
intrā me deus est, the Lord is within me
intrā iactum telī, within a javelin’s throw (denoting distance)
Intra + accusative of time is one ways of denoting the time within something occurred.
intrā quattuor annōs, within four years
intrā lucem, before the day was done
intrā diēs paucōs, within few days (before a few days had passed)
intrā morae breve tempus, without a moment’s delay
It can also mean less than a given duration or quantity.
intrā centum fūnera fēcit, he inflicted fewer than 100 casualties
intrā trēs diēs abiit, he left before three days had passed (compare above)
2. Diēs is typically masculine (like most fifth declension nouns), but is occasionally feminine, especially in fixed phrases and general reference to time or dates.
cōnstitūtā diē : on a fixed day
longa diēs intervēnit : a long time had passed
3. Diēs is one of only two nouns in the fifth declension that is entirely declined. Rēs is the other such noun—all other fifth declension nouns are wanting in the plural (or at least the plural genitive, dative and ablative) in extant Latin literature.
Quite closely relate to expression of existence / non-existence are expressions of past time, which make use of the phrase est cum and fuit cum, which may be translated as ‘there was a time when…’ Like the phrases that describe existence, these make use of a relative clause of characteristic (w/ subjunctive!) to describe an indefinite period of present/past time.
est cum …. present subjunctive
fuit cum …. imperfect subjunctive
est cum in omnis virī aevō domum parentis linquat: there comes a time in every man’s life when he must leave the home of his father
est cum omnibus deceat: there is a season for all things
fuit cum mihi quoque initium requiēscendī fore iūstum arbitrārer: there was a time when I thought a beginning of rest would be justifiable on my part
fuit cum nōn altior meīs genibus essēs: there was a time when you were no taller than my knees