It occurred after Operation Combination and before G-2.
I see you were reading their Cybertron (planet)
On this timeline page
, however, under the section titled "After 2025", it gives the following line of text:
Planet Cybertron is revived, but suffers a deadly energy shortage. Optimus Prime becomes a Powermaster, fuses with a Nebulan, and protects himself with a phase modulation shield. He enters a black hole to get the super energy Nucleon.
with a citation of "Nucleon Quest Super Convoy's toy bio".
The toy bio in question reads as follows:
Background: Once there was era in which the planet Seibertron had been struck by a fatal energy shortage. At this time, Convoy and Hi-Q, a scientist from the planet Nebulos, undertook a perilous journey in search of a new energy to replace Energon.
Abilities: In order for him to extract the super-energy "Nucleon" that exists in black holes, his entire structure is now protected by a phase modulation shield. He can now carry out activity in super-gravitic environments.
Personality: A protector of freedom, he possesses enormous intelligence and courage.
Weapons: Concussion blaster, twin particle beam cannons
How this toy bio fits into the timeline is like this. In 2006-2007, TakaraTomy produced two timelines in two Kiss Players reference books. Both of these timelines took a lot of fiction and grouped them together in an attempt to form a single, coherent timeline. This included the Nucleon Quest Super Convoy toy bio, which was placed between Operation Combination and G-2. These timelines also added additional information written by the author directly for the timelines to help make things work, and the bit about Cybertron being restored with Nucleon was likely one of these newly-added bits. Therefore, the source for Cybetron's restoration comes from the timelines themselves.
A translation of these two timelines (merged togehter as one) can be found here
. As you can see, the Wiki's timeline page is very much based on the source translation page, but with additional content added to it and the Binaltech story bits given their own sections to split them from the main timeline.
Hope that helps.