The indexing in Alfresco is asynchronous and the indexer runs every 10 seconds so there will be an average delay of 5 and a bit seconds between a document being added and it being indexed. It could be emuch longer under heavy load or with lots of document additions.
Alfresco can also use a thing called "intransaction indexing" if you have it enabled and use the appropriate query subset. This uses the database not Lucene (Solr) and so it much more "instant".
There is little you can do about the latency but you can try and use query syntax & languages that exploit "in transaction indexing".
There is some explanation of the subset in these forums.