Unstable Time
Active challenge.
Timing on this challenge can vary wildly, as this can take more than 24 hours at ~e126 mysteries, but at higher mysteries and attributes, it can be done much faster, down to about 15 minutes.
You can do this challenge much faster if you do a lot of the reduce level requirement by 1 challenges. Also get Intelligence 75 and Mastery 125 (both reduce level requirements by 1). This is a huge time saver. The lower you can lower this the faster this challenge will be.
Strategy
You start as an apprentice; when you are switched, you are either a Prodigy or Chronomancer. Often, you will be reassigned a new pet. You can manipulate your class between Prodigy and Chronomancer and which pet you are using by casting your lowest cost spell, Spell Focus, repeatedly to force completions and attempting to reroll the selection. Note that if you get Devourer or Hungerer, prioritize casting Spell Focus and getting rid of it, because they can hurt your progress. Daemon won't get experience without a Demonologist spell.
You need to be active and stay in control. When you get a configuration of class and pet that you want, avoid casting unnecessary spells, because each spell completion is a potential reconfiguration. Mostly avoid autocast, although, I found autocast useful on Ley Apex when I was fulfilling that requirement.
You will need a source of shards. Keep one autoclick summons going for shards; I recommend 
Conjure Manabeast. In this challenge, long summon duration benefits you, since you'll have less random end of spell chances to deal with.
Do the 
Ley Overdrive casting requirement first. The two casting requirements cannot be undone, so they are good to get out of the way. Of the two, Ley Overdrive is easier to attain and casting it will not directly increase the difficulty. If you have 
Shadow-Scryer's Crystal Ball, you can equip it to reduce Ley Overdrive's duration by casting 3 evocation spells alongside while it's active.
Do 
Time Helix next. Time Helix will reset both Class and Pet XP, to the point where you will have to level again to recast it. A Geode pet or Ley Keeper will lower the level requirements which can speed the completion up. Highly recommended, even though you will have to reacquire the Geode from time to time; minutes of rerolling vs hours of waiting.
When you are done with the two spell cast requirements, you just need to level you and your pet. Different pets level differently, some are faster than others. Read their description and find one(s) you like. 
Spellhound is one of the easiest pets to level, which gains XP when it yields shards. You can focus on farming Pet XP spells that appear randomly; cast them as soon as you get them, or they will disappear if your class changes.
For character levelling, buy all available sources, keep the autoclick going for shards, also focus on collecting Void entities. Click manually, you don't need the Void Automaton, you have to do this actively anyway, and it's best to not cast needless spells. That said, A 
Void Lure or equivalent like 
Void Syphon if it pops up can be worthwhile, since it can greatly affect the available void entities to click.
True Sorcery helps a lot to speed up your level, especially if you've used it in the past, as the level gain is persistent. When you are finished with the other goals, you can low cost cast to get Prodigy, and switch to True Sorcery to get the required character level.
Attributes
- 25 Intelligence
- 25 Insight
- ~ Wisdom
- ~ Patience
- ~ Dominance