Adjectives

(s)ill-timed, unseasonable, untimely, wrongbadly timed“an ill-timed intervention”, “you think my intrusion unseasonable”, “an untimely remark”, “it was the wrong moment for a joke”
(s)premature, untimelyuncommonly early or before the expected time“illness led to his premature death”, “alcohol brought him to an untimely end”

Adverbs

(r)prematurely, untimelytoo soon; in a premature manner“I spoke prematurely”