The time frame of the class content has nothing to do with its rigor. Typically, college-level US history surveys are semester-long classes that cover either the first half (up to/through the Civil War or Reconstruction, depending on where that particular department divides the courses), and the second semester picks up there and goes to the present. So APUSH is a full-year class that covers the equivalent of two college semesters’ worth of content (though if your AP score qualifies you for college credit, you’ll only get one semester of credit). The DE course is a college-level semester course that covers one half of the US survey or another, and if you get college credit, you’ll get a semester’s credit, just as with the AP. But the pacing of the courses is the same – the AP classes covers two semesters of college content in two semesters, and the DE class covers one semester of college content in one semester.
The difference is standards. Typically, the AP classes demand more reading and writing, and more rigor in testing, than DE classes do (or course, this may vary). And the AP classes are built around a nationally recognized thematic framework and exam, whereas DE classes are not. This is probably why AP classes are recognized nationally, though each college decides whether a passing score on the APUSH exam gets you college credit, an exemption from prerequisites, or nothing. A DE credit is more likely to count as transfer credit at an in-state public university (it’s the equivalent of taking the class at a community college, which would count as transfer credit based on a passing grade) but not guaranteed at private or out-of-state universities, which might be less likely to accept those transfer credits.