How to enforce promissory note

Absent an agreement by both sides to another forum (such as the American Arbitration Association), there is no legal way to enforce any contractual obligation other than by suing on it.  It is hard to estimate how long the litigation will take because it may depend on what defenses the debtor may have and how hard he wants to fight the claim, i.e. how much money he is willing to spend.  If the debtor has a meritorious defense, and is willing to spend the money to engage in motion practice, engage in extensive discovery, etc., it can be quite a drawn out process.  Alternatively, if the defendant has no real defense which requires a trial, and/or is unwilling to spend the money to litigate the dispute to its fullest, the matter can be resolved by a Court relatively quickly, perhaps within a few months, or even quicker if the parties reach a settlement.