The exterior shot of Diane's residence shows it to be light outside when she and Sam enter and turn on the lights, but when the camera switches to the interior moments later, it appears to be completely dark outside.
Rhea Perlman became pregnant during Season One, and her character Carla Tortelli also became pregnant. Perlman gave birth before shooting for Season Two began; Carla Tortelli was still pregnant for the first two episodes, and the fake baby bump is obviously smaller than Perlman's genuine Season One baby bump.
Sam says he's never been in Diane's apartment. However, in an earlier episode Sam and Carla helped Diane home after she passed out from the effects of Carla's powerful cocktails.