Your probably fine….. kids at my high school will run their 5 stud cars with 2 missing lugs on multiple wheels for weeks. I’m not joking when I’m saying this, kids are so silly. If they can do it, I’m sure you can do it too.
To me the question is why is it missing in the first place. If your mechanic has a habit of over tightening lug nuts to the point that one of the studs has broken, then it might be time to replace all the studs and nuts and find a new mechanic. If there is a reason why one is missing or you are sure that there has not been some systematic carelessness applied to your wheel mounting, then you should be OK.
Don't put it off; fix it when you can. It may be okay for 5 years... and it may loosen up the other bolts and/or nuts and cause your front hub assembly to suffer serious damage and/or have your front wheel come off to under speed.
I had a loose lug nut which allowed the wheel to wobble when I turned hard left. After a few days it caused the lugs to wallow and BORE a hole THROUGH the hub which finally gave out when I was pulling out of a parking space on my 18th birthday. I knew it was a problem and I had brought it to my dad’s attention who said it would be fine till the weekend when we could take a look at it. Didn’t make it to the weekend.