I know that one can buy the plugin LRTimelapse for use with Lightroom 6 in the production of timelapse videos; my question is, is it required to make timelapse videos with Lightroom 6?
Yes, you can manually set the slide duration a slideshow to be 0.04s (25 fps). However, I've found that the resulting product isn't as good as other methods of stitching together timelapses.
Yes, LR can produce timelapse without preset. But it'll select the default fps which is more than 30fps. Your timelapse will look like a slide show, not like a video you are expecting. I think LRtimelapse.zip file is available online for free. It has 23, 24, 30 fps presets.