Does diazepam taken on day interfere with general anasthetic drugs? To make ga last longer or misjudge dose etc?

The regular use. Of diazepam or even alcohol in the past means your liver and metabolic activity are revved up and they have to adjust the dose of anesthesia for your need and the length of surgery as you may wake up from the anesthesia sooner.
Depends on dose. A small valium (diazepam) dose won't make much difference. Taking a lot of valium, ativan, xanax, (alprazolam) or any other sedative changes how your body metabolizes other drugs. Tell your physician anesthesiologist about all meds you take so your anesthesia can be tailored to you. Same is true for alcohol, "recreational" drugs, and over-the counter meds. Honesty is best policy! good luck--.