It's an open event, but the Chess.com Isle of Man International is extremely strong - have a look here at the top 20 playing in the Masters event. The action starts at 1:30 p.m. local time (= 8:30 a.m. ET, or 90 minutes after the start time for the World Cup). It's a smooth transition from one super-event to the next.
In fact, this tournament, like the World Cup, is a big deal for the 2018 Candidates, as Vladimir Kramnik and Fabiano Caruana - who are playing - are competing with Wesley So - who is not - for two ratings slots in the latter event. So there's plenty at stake here in addition to the prize fund, bragging rights in a tournament with Magnus Carlsen, and all the other usual competitive aims the players may have.