quoque dies

In LLPSI Cap XX: Iulia: 'Noli a nobis discedere! Vel si necesse erit domo abire, non modo tertio quoque die, sed cotidie ad nos reverti debes.

What does ‘quoque die’ mean? ‘…non only on the third day but every day you must return to us…’ ??

“tertio quoque die”
Vide: http://discourse.textkit.com/t/tertio-quoque-verbo/10902/1

Gratias tibi ago.

It would be worth adding that quoque is postpositive; it never refers to the word after it.

I guess, therefore, it means each third day…

By the Roman reckoning, yes. But, since they counted both the first and last day, whereas we don’t count the first, it translates as “every other day”.

For example:

Wednesday is two days from Monday in English, because we count only Tuesday and Wednesday. But, in Latin, it is three days from Monday, because they count Monday, Tuesday and Wednesday.

Gratias tibi ago.