How does Song of Freyalise chapters 1-2 work?
According to the wording of this effect, my creatures will gain the {T} ability until end of turn or no?


Not exactly. The card says 'Until your next turn', so that means you can use their mana ability during your opponent's next turn (or turns, if it's a multiplayer game or they cast Time Walk) as well. Only when it's your turn again will the effect stop.