late Old English mistimian "to happen amiss" (of an event); see mis- (1) "badly, wrongly" + time (v.). Meaning "not to time properly, say or do inappropriately" is from late 14c. Related: Mistimed; mistiming.
prefix of Germanic origin affixed to nouns and verbs and meaning "bad, wrong," from Old English mis-, from Proto-Germanic *missa- "divergent, astray" (source also of Old Frisian and Old Saxon mis-, Middle Dutch misse-, Old High German missa-, German miß-, Old Norse mis-, Gothic missa-), perhaps literally "in a changed manner," and with a root sense of "difference, change" (compare Gothic misso "mutually"), and thus possibly from PIE *mit-to-, from root *mei- (1) "to change."
Productive as word-forming element in Old English (as in mislæran "to give bad advice, teach amiss"). In 14c.-16c. in a few verbs its sense began to be felt as "unfavorably," and it came to be used as an intensive prefix with words already expressing negative feeling (as in misdoubt). Practically a separate word in Old and early Middle English (and often written as such). Old English also had an adjective (mislic "diverse, unlike, various") and an adverb (mislice "in various directions, wrongly, astray") derived from it, corresponding to German misslich (adj.). It has become confused with mis- (2).
Old English getimian "to happen, befall," from time (n.). Meaning "to appoint a time" (of an action, etc.) is attested from c. 1300; sense of "to measure or record the time of" (a race, event, etc.) is first attested 1660s. Related: Timed; timing.
Others are reading
<a href="https://www.etymonline.com/word/mistime">Etymology of mistime by etymonline</a>
Harper, D. (n.d.). Etymology of mistime. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/mistime