code: func (b *BlockChain) isCurrent() bool {
  	// Not current if the latest main (best) chain height is before the
  	// latest known good checkpoint (when checkpoints are enabled).
  	checkpoint := b.LatestCheckpoint()
  	if checkpoint != nil && b.bestChain.Tip().height < checkpoint.Height {
  		return false
  	}
  
  	// Not current if the latest best block has a timestamp before 24 hours
  	// ago.
  	//
  	// The chain appears to be current if none of the checks reported
  	// otherwise.
  	minus24Hours := b.timeSource.AdjustedTime().Add(-24 * time.Hour).Unix()
  	return b.bestChain.Tip().timestamp >= minus24Hours
  }
docs: // isCurrent returns whether or not the chain believes it is current.  Several
  // factors are used to guess, but the key factors that allow the chain to
  // believe it is current are:
  //  - Latest block height is after the latest checkpoint (if enabled)
  //  - Latest block has a timestamp newer than 24 hours ago
  //
  // This function MUST be called with the chain state lock held (for reads).