The run's clock is simple: one wave is 60 seconds. A look at the wave counter also tells you how many minutes you've survived.
A Wave Is a Minute
Every wave lasts 60 seconds, so if you're on wave 10, you're around the ninth minute. As the waves go on, both the number of enemies and their toughness go up.
A Boss Every Five Minutes
Bosses arrive on waves 6, 11, 16, 21, 26 and 31 — on the clock, 5:00, 10:00, 15:00, 20:00, 25:00 and 30:00. The gaps are always exactly five minutes, so you can time your preparation around them.
After a Boss Dies
Three things happen in order: first a relic drops, then the route choice opens, then you move on to a new sector. So you collect your reward first, then decide where to go, and the map changes last. The biome never changes on its own — you have to kill the boss to move on.
Loops
When you finish every biome, you go back to the start, but the game gets harder: each loop, enemy health rises by 35%, damage by 18% and speed by 6%. Past the thirtieth minute, staying alive depends on how well your build scales.
Since you know when the bosses come, plan your terminal visits around them: spending the essence you're holding a few waves before 5:00 always beats walking into the boss unprepared.