Stoneblood

Once you get to 27 - 30 mill timecubes, stop doing long runs and start overpower-runs.
--> maxed starting gold
--> maxed time cube dropped and time cube gained
--> 5 waves to be defeated
--> starting wave between 741 and 991, takes 20 - 30 minutes till wave 1800 where overpowered wares out.
No effort, between 2000 and 4000 time cubes a minute depending on your starting level and your stop level.

Just a hint:
- Get weapon cubes as soon as you can and invest in auto clicks
- Get some starting gold and keep your starting level low, so you can get overpowered status. If you have enough Active Ability time (aim at minimum +12 seconds), you can get a nice long ability timer that lasts a while and gets you levels quickly without effort. If your starting level is low, you can get a a times of +1h with ease.