This is a Small Claims forum. If the OP is questioning something about a SC case, he/she is going to have to appear in court on the hearing date to get a default, regardless of the date of service. If the question pertains to a case in SC or a higher court, the clerk is going to be prohibited from saying anything that might be remotely construed as “legal advice”.
To the OP – assuming this is not SC and the defendant was personally served and the time for response is 20 days, time starts running on the date of service and a default is available on the 21st day thereafter. However, where service was made, how service was made and the nature of the action can all affect the timeframe. Since you haven’t supplied much information, you would be best served by consulting your process server.