As a rule of thumb, jams without pectin do not set as readily as those with pectin. Adding a small quantity of tomato purée or apple sauce to apricot jam will provide this critical set point.
It doesn't need it to set, but it may take longer because the sugar and fruit aren't as acidic as fruit used for jellies. If your recipe doesn't tell you to add anything like that, ask the person who has made the recipe before....