Dui after Sf86 submission

Hello,
My friend recently came to me for advice and I don’t know if I gave them the correct answer. Here is the situation, My friend just graduated college and received a job offer for the federal government working in Aerospace Engineering, he filled out the SF 86 and submitted it as requested and received his final offer a few days later. He was super excited about the new position and went out with friends and ended up being charged with a DUI (misdemeanor no aggravating factors and compliant) He accepted the offer and is getting ready to report to duty. Today someone contacted him for a personal interview for his security clearance. My friend has had no other run ins with law and has hired lawyers to deal with his case. So, it may be a while before any kind of resolution. I told him to just be totally honest with the investigator at his interview and make it clear that all of this happened after his SF86 submission. Is there any other advice that should be given? I hate that this happened to him he is such a good person. Huge mistake but it may take time to prove that he isn’t a problem. Will this delay his clearance? Is there anyone else he should tell about his situation before arriving for his first day on the job?