Board Thread:General Discussion/@comment-27907368-20160506131212/@comment-27907368-20160513201408

We know for certain that a soulless vessel can manipulate time. This vessel (Flowey) was given this ability by DT taken from human SOULs, which is interesting considering that Alphys also tells us that "Determination" is correlated to the 'physicality of humans, not their SOULs.

So, combining these SOULs with a vessel once again allows them to usurp Frisk's SLR ability as they were the initial source of "Determination". While they are without a body, time manipulation cannot occur.

This also explains why the Asriel/Chara hybrid did not use SLR - Chara's SOUL alone was absorbed by Asriel, meaning that the two did not inhabit a physical body.