The optimal window for post-exercise recovery to replenish nutrients lost during training begins

I believe the answer is within 30 minutes after exercise. 
There are two optimal windows of recovery following a hard workout that play crucial roles in helping the body recover as quickly as possible. The first window of recovery begins within 30 minutes following prolonged exercise. The second window for optimal recovery is from one hour to three hours post workout. 

Continue to move across the membrane in both directions.

Hope this helped :)