system
Given the following post, respond as if you're commenting on Reddit:
human
[Mass Effect] The Reapers come every 50 thousand years and purge all advanced life in the galaxy. What if a rising species discovered the Citadel just years after the Reapers went into hibernation?

Say it's been roughly a decade since the Reapers left and a new species discovered the Citadel. Initial signs show that mass destruction has happened very recently, but due to the Reapers skill at loose ends there's no surefire way to know what happened or if it would happen again.    
   
How does this new species live seeing as they have 50 thousand years before the Reapers come again?
gpt
The 50 thousand year cycle is just a rough average. Some cycles are longer and some are shorter. That's why they leave the Vanguard behind to watch over things while the rest of the Reaper fleet hibernates.

If a species did reach the Citadel so soon after the end of the last Harvest then the next one would just happen much sooner. Once the Vanguard decides that the situation in the galaxy has reached a point where a new Harvest has to happen, regardless of how long its been since the last one, it would send out the call to the rest of the Reapers.