The HDR Timelapse mode combines the time-lapse with HDR (High Dynamic Range) mode. In other words, each frame of the time-lapse video will be an HDR photo.
This can be a complex goal to achieve, but the HDR Timelapse mode takes care of it very easily. This mode divides the screen into two parts. The upper part of the screen is about the time-lapse parameters. You can set the Interval value and the number of photos required for the time lapse video. The lower part of the screen shows the HDR settings The HDR part has three parameters to be adjusted, Center, EV(+-), and Frame.
Center: This parameter shows the exposure value that will sit in the middle of the sequence.
EV(+-): This parameter shows how many stops each change will be.
Frame: This parameter shows how many pictures are to be taken for an HDR photo.
For the limitations of the HDR Timelapse mode, please see the warning in the HDR Mode section.