Under Maryland lien laws, a mechanics lien must be filed within 180 days of the claimant's last date of furnishing labor and/or materials to the project. Once that deadline passes, the right to file a mechanics lien claim also passes. However, there are still other options for recovery against your customer such as breach of contract, unjust enrichment, or claims under Maryland's prompt payment laws.
Here are some resources that dive into these options more: