- Septem horis ad eam urbem venimus.
septem horis: ablative plural feminine; this is an example of the "ablative of time within which".
eam: accusative feminine singular from is, ea, id. Here, eam is used as a demonstrative (rather than as a personal pronoun); and it agrees in number, case and gender with urbem. It is accusative because it follows the preposition ad.
urbem: accusative singular feminine of urbs, urbis.
Remember that urbs is one of the 3rd declension "I"-stem nouns, so the genitive plural adds an "i" (urbium).
venimus: 1st person plural perfect active indicative from venio, venire, veni, ventum.
In fact, when you come across venimus in a text, the only way you can tell whether it is perfect or present active indicative, is by looking at the "e": if it is short (no macron) then it is present; if it is long (with a macron) then it is perfect. In Wheelock, you will see a macron over the "e" in this sentence; but no macron has yet been located online, so imagine it there! Besides, try using a present in this particular sentence, and it just won't work.
Within seven hours we came to that city.
- Italia illis temporibus erat plena Graecarum artium, et multi Romani ipsi has artes colebant.
illis temporibus: ablative plural neuter. This is an example of the "ablative of time when".
Graecarum artium: genitive plural feminine. It is in the genitive, because it follows plenus: that is, in Latin, plenus takes a genitive; we do the same thing in English: "He's full of nonsense".
Remember ars, artis is an "I" stem noun of the third declension; so it has the "i" in the genitive plural.
ipsi: nominative plural masculine of the intensive ipse, ipsa, ipsum. Here, ipsi intensifies multi Romani, so it agrees with it in number, case and gender.
has: accusative feminine plural of the demonstrative hic, haec, hoc. Here, has is a demonstrative adjective, modifying artes; so it agrees in number, case and gender with artes.
colebant: 3rd person plural imperfect indicative active.
In those times, Italy used to be full of Greek arts, and many Romans themselves used to cultivate these arts.