Timer triggerBatchTimer = new Timer(() => yourBatchBlock.TriggerBatch());
TransformBlock<T, T> timeoutTransformBlock = new TransformBlock<T, T>((value) =>
{
triggerBatchTimer.Change(5000, Timeout.Infinite);
return value;
});
timeoutTransformBlock.LinkTo(yourBatchBlock);
yourBufferBlock.LinkTo(timeoutTransformBlock);