By flipping through the footnotes of the Source Chrétiennes volume, I found a few other contemporary references.  They are frustratingly scant, but I offer them to you nonetheless.

On page 234 of the SC volume we have the following text in Latin,
"Potest hoc et in tempore persecutionis gentilium de sanctis martyribus et confessoribus aptari.  Considerant enim impii persecutores unumquemque iustorum et quaerunt mortificare eum.  Sed ne securum reddat pacis tempore ista talis expositio, memento quia cotidanum habet iustus persecutorem diabolum et ille est qui considerat iustum."

"This scripture (“You would have no power over me, if it was not given you from on high”) can be applied to the holy martyrs and confessors in the time of the persecution of the nations.  For the impious persecutors carefully examine each righteous one, and seek to kill him.  But so that this speech, in this time of peace, may not render you secure, remember that every day the righteous one has a persecuting devil, and this is the one who always plots against the righteous." (Hom. In Ps. 36 V, 4.11)

Crouzel and Brésard note, "The life of Origen passed between periods of persecution and those of calm.  The text here envisages these two alternatives.  It appears that these homilies were delivered in times of peace, probably under Philip the Arab, the first Christian emperor, before the great persecution of Decius."  (p. 234n2).

They are much more cautious this time.  Philip the Arab was certainly sympathetic to Christians, even if not the "first Christian emperor" as they claim.  Philip reigned from 244 – 249, so they would date them tentatively to this period.  This seems plausible, but there are other plausible schemas too.

Another reference, seemingly at odds with the first, comes later.

"Obmutui et non aperui os meum, quia tu es qui fecisti.  Iam et hoc superius exposuimus, cum tractaremus illum versiculum qui ait: Dum consistit peccator adversum me, obmutui et humiliatus sum et silui a bonis.  Bonum et enim eo tempore com adversum nos vel derogationum conviciorum vel probrorum tela iaciuntur, nos huius versiculi meminisse, qui ait: Obmutui et non aperui os meum, quia tu es qui fecisti." (Hom. In. Ps. 38 II 6.3, pg. 388)

"I was silent and did not open my mouth, for you are the one who has done it.  We explained this earlier, when we examined that verse which said, "Then the sinner stood against me, I was silent and humiliated and refrained from speaking good.  For it is good in this time, when weapons of defamation, or injuries, or slander are thrown against us, to remember this verse which says, "I was silent and did not open my mouth, for you are the one who has done it."

Crouzel and Brésard note, "We saw earlier (ie, the earlier note in this post) that these homilies must have been delivered in times of peace, perhaps under Philip the Arab, the first Christian emperor (Cf. H. Crouzel «Le christianisme de l’empereur Philippe l’Arabe», Gregorianum 56 (1975), p. 545-550).  This allusion to defamations could relate to the time, under the same emperor, in which the millenium festivities of the foundation of Rome were celebrated (247-248), which caused a renewal of patriotism and attachment to the traditional religion, and led to the subversion of the Christian emperor of the four rivals, one of which vanquished and killed him.  The was the emperor Decius, who initiated the first truly empire-wide persecution." (p. 388n3).

Again, this strikes me as plausible, but not certain.  Certainly, defamations and slanders are not mutually exclusive with a time of offical peace towards Christians.  And yet, it would probably be difficult to find a time before Constantine (and perhaps after!) when there weren’t "defamations" of these types. 

So far we have an illusive 30 years reference, and a time of peace.  Unfortunately, these passages don’t appear to have been preserved in the newly discovered manuscript, so we don’t have the Greek to check.

ἐν αὐτῷ,