It is said that the Cherub's session is only winnable by a Lord of Time, then I was thinking, couldn't Calliope just teleport herself on each planet to stop the detonations? Her aspect is Space after all.

Bold of you to assume Callie could teleport or Caliborn could time travel that early into their Quests. It’s highly likely more Caliborn’s overall thing where the Timeline just falls in his favor- 3 Planets down from the start for example- As well as his own ultra-determined forward momentum and the minions he gathered from each Planet having Timey Shenanigans.