There is adequate documentary evidence to show that the Manichaeans were indeed acquainted with the Gospel of Thomas and used it (cf. the many parallels in the Manichaean Psalm Book), but I highly doubt Cyril of Jerusalem knew anything about the book's actual authorship and was interested mainly in impugning its reputation to prevent others from reading it. As it is, the book does not look like a Manichaean composition per se and it lacks distinctive Manichaean ideas. On the other hand, Mani himself was influenced by the Mandaeans and the Elkasites and likely adopted literature current among them (as he reportedly did with a wide range of literature including Persian and Indian texts); in fact, the Acts of Thomas was also adopted by the sect, which has a different background than the Gospel of Thomas, suggesting that they accepted Thomasian literature in general as scripture (cf. Mani referring to The Twin as the source of his revelation).
The Naassenes apparently had a more developed gnosticism than expressed in Thomas (as were the Manichaeans), if the Naassene Fragment is anything to go by, yet they too likely adopted a pre-existing proto-gnostic text as scripture, or possibly modified it in their own community. The two texts paraphrased by Hippolytus (5.7.20, 5.8.32) bear some striking resemblences to the Greek and Coptic recensions of Thomas. The first one appears to be a garbled conflation of Thomas 2, 4, and 77:
Hippolytus: "One who seeks (ho zétón) will find me (eme heurései) in little children seven years old (en paidiois apo etón hepta), for there, hidden in the fourteenth age, I am revealed".
Thomas 2: "Let one who seeks (ho zétón) to continue seeking until he finds (heuré)".
Thomas 4: "A person old in days will not hesitate to ask a little child seven days old (paidion hepta hémerón) about the place of life, and that person will live."
Thomas 77: "Lift up the stone, and you will find me (heuréseis me) there. Split the piece of wood, and I am there".
The other text cited by Hippolytus is clearly Thomas 11:
Hippolytus: "If you ate dead things (nekra ephagete) and made them living (zónta epoiésate), what will you do if you eat living things?"
Thomas 11: "The dead are not alive, and the living will not die. During the days when you ate what is dead, you made it alive".
The same thought is contained in Thomas 7, the logion about the lion becoming human when eaten by a man, as well as in Thomas 60 which warned against becoming eaten like a carcass. These parallels (unattested elsewhere concerning little children seven X old and making dead things living by eating them) are imho sufficient to show that the Gospel of Thomas known to Hippolytus was a version of the gospel attested at Oxyrhynchus and Nag Hammadi.
BTW, shortly after Hippolytus wrote concerning the Gospel of Thomas used by the Naassenes, Origin (in AD 233) also noted a "Gospel according to Thomas" (alongside a Gospel of Matthias) was popular in Egypt, suggesting a wider circulation than the Naassenes or the later Manichaeans (Manichaenism did not reach Egypt until AD 244).
All in all, a second-century date is most plausible to me, i.e. c. AD 150, tho a date shortly before AD 135 is quite attractive owing the proto-gnostic outlook and lack of distinctive Basilidian, Valentinian, Marcionite, or Sethite ideas (found virtually everywhere else in the Nag Hammadi corpus, aside from the secular tractates)...