^ Sounds like Master of Evil will essentially begin with Vader bleeding his kyber on Mustafar(as detailed in Darth Vader v2 #1-5.) Then [in the comics] Vader returns straight back to Coruscant to show off his shiny new red blade, and heal/recover from the injuries he sustained -- then he immediately undertakes a few more brief missions(as detailed in issues #6-12 of the same series.) *Note: all of this takes place just days/weeks after RotS.* Then, at the beginning of issue #13, we learn that roughly 1 year has passed since the conclusion of issue #12 and the Empire's ascension... So I'm guessing(?) the majority of this novel will be set in that ~1 year gap of unexplored time(so vastly pre-prime Vader, I'd assume, but that's neither here nor there.) /shrug
Assuming MoE follows the existing timeline, then it'll take place a good bit before Lords of the Sith, yeah. As mentioned: we know this novel basically starts at Vader bleeding his kyber, which canonically occurred just a few days after RotS. LotS, however, is set in 14BBY(ie. years after RotS.) So MoE will feature a Vader who is still trying to acclimate to his armor, still adjusting to his new life as a near-crippled/disfigured Sith, still figuring out his status within the newly-formed Empire, still trying to erase the concept of "Anakin"(ie. the good) within himself, etc. Vader should be extra hateful/bitter/sadistic in this, tbh.
*That said, it's also possible(though unlikely, given the summary) that MoE will start a few days after RotS, but then cover a huge chunk of time by its conclusion. Again, we'll just have to wait and see.