That's an interesting question. First, under § 8550 of the California Civil Code, a claimant may commence an action to enforce payment of the claim in a stop payment notice, but the enforcement action must be filed "not later than 90 days after expiration of the time within which a stop payment notice must be given." That deadline will depend on who hired the party sending the stop payment notice. For a direct contractor, a stop payment notice must be sent by the earlier of the following two dates: (1) 90 days after the completion; or (2) 60 days after the owner records a notice of completion/cessation. When a stop payment notice is being sent by someone other than a direct contractor, the time frames change a little. For these parties, a stop payment notice must be sent by the earlier of the following dates: (1) 90 days after the completion of the project; or (2) 30 days after the owner records a notice of completion/cessation. Thus, the deadline to "enforce" (file suit) on a stop payment notice will be 90 days after the filing of the stop payment notice, and the deadline for sending that notice may vary depending on whether a notice of completion or cessation was filed, and depending on the claimant's role on the project.