If we guarantee in writing that the product will deliver by a certain date and then the actual delivery happens past that guaranteed date can that affect our ability to file a lien for payment?
Probably not. If you miss the date you may be in breach of the contract. But if you ultimately deliver the materials and then are not paid for them, you would still likely have a lien right against the property. You may want to consult with an attorney to see if your delivery date has any other impact on your contract or lien rights.