If you were given a suspended sentence, then you are asking to vacate your record of conviction. If you were convicted of a non-DV assault, then you must wait 3 years after completion of the terms of the sentence. Five years if the victim was DV related. Often times the suspension period of a sentence is two years, so that will be 5 or 7 years after you were sentenced in court.
If you were given a deferred sentence, the above will not apply, you will need to expunge records of your previous conviction.
JensenLegal.com handles these cases. I rarely see someone do this without the assistance of an attorney. (206) 617-9173