retrofit-mock/src/main/java/retrofit2/mock/NetworkBehavior.java
public void setDelay(long amount, TimeUnit unit) {
    if (amount < 0) {
      throw new IllegalArgumentException("Amount must be positive value.");
    }
    this.delayMs = unit.toMillis(amount);
  }
public void setDelay(long amount, TimeUnit unit) {
    if (amount < 0) {
      throw new IllegalArgumentException("Amount must be positive value.");
    }
    this.delayMs = unit.toMillis(amount);
  }
Set the network round trip delay.