At the start, keep your autobuyers as they normally are, until about 48 galaxies where you pause all your autobuyers (press A).
Get the next galaxy, then set your dimboost autobuyer to 1 second and turn off buy max. Manually get the first dimension boost, then press M once, and spam (not hold!) 5 until you get equal or just over the required next dimboost.
Repeat this until boosts = 2 * galaxies (mod 5), i.e. if your galaxies end in 0 or 5, get 5 or 10 boosts (or any number ending in 0 or 5), if it ends in 1 or 6, get 2 or 7 boosts, if it ends in 2 or 7, get 3 or 8 boosts, if it ends in 3 or 8, get 4 or 9 boosts.
If at any point you accidentally press M, SET 5TH DIM TO BUY SINGLES then turn on your dimboost autobuyer for one reset (5 boosts) by pressing A twice in quick succession. TURN IT OFF IMMEDIATELY AFTERWARDS. Then correct your boost amount.
When this is done, make sure your 5th dim is now set to BUY MAX. Press A (toggled on) again, and wait until your boosts are equal to twice your galaxies. At this point, press A (toggled off), hold M if needed, and get the next galaxy. EXPORT YOUR SAVE REGULARLY.
The challenge is completable at around 60 galaxies.