This sounds like the usual bluster that gets everyone in a tizzy. Kim can't get out of this without looking weak and upsetting China, and he can't afford that.
Kim is working the Moon side of the deal. He is seeking to drive a wedge between Trump and SK. He may succeed, Trump is set for military drills and Kim has already agreed that delaying the drills is not an issue with the summit, but it could be an issue with a Moon - Kim meeting, and it may succeed. To me this is a small concession to allow NK to save some face. (His own people and ego are threatened by his willingness to give up his nukes.) But it is still by far the best outcome for his regime. (If he is smart enough to see this.)
As far as the US is concerned, if SK wants to delay drills for a month, we probably should let them. But all sanctions are still in force and Kim gains little from Trump with this maneuver.