Average Days on Market (DOM) is a measure of market velocity - how long it takes homes to sell. A non-seasonal increase in DOM could indicate some softness in the market; a drop in DOM points to a market that’s heating up.
DOM typically starts falling at the end of March during the peak buying season of April through June, then starts to climb in the second half of the year. However, this seasonal trend can vary depending on the market and the unique seasonal attributes of the area - for example, Phoenix has a different buying season than Detroit.
Look at a couple of years of your market’s data to determine what’s “normal” for your area in each month.