Legal Question in Civil Litigation in California

You conveniently leave out the provision that the deadline is 45 days from the responses OR any supplemental responses. Feel free to try to stand on the 30-days. IF the court thinks your responses are sufficient, the court may decide the 30-day agreement supersedes that code 45. But if you are screwing around and giving incomplete and/or evasive responses to interrogatories, the court is going to hold the 45 days applies and not only order further responses, but also make you pay the other side's attorneys fees for forcing them to bring a motion. Bottom line: don't try to use technical arguments to avoid legitimate discovery response obligations. There is nothing the court likes less than discovery gamesmanship, and they will throw the book at you if you are not being fully compliant with your discovery obligations.

You are misreading the statute. Code of Civil Procedure section 2030.030, subdivision (c) states that "[u]nless notice of this motion is given within 45 days of the service of the response, or any supplemental response, or on or before any specific LATER date to which the propounding party and the responding party have agreed in writing, the propounding party waives any right to compel a further response to the interrogatories."

Thus your opponent has 45 days from service of the supplemental response to move to compel, unless you agree in writing to a LATER date. It doesn't say you can agree to an earlier date.

Finally, I agree with Mr. McCormick that it appears you are engaging in gamesmanship, which is a quick way to lose your case.