The definition of "premeditation" is somewhat ambiguous and can easily be misleading. The legal definition of "premeditation" is with planning or deliberation. However, the amount of time needed for premeditation, regarding any act, depends on the person and the circumstances. After forming intent, the time must be long enough to act, and it must also allow for the person to have been fully conscious of the intent and to have considered the act.
As far as I know, you must have prior planning to have premeditation. Hence, in this case that lacks: a clear and unyielding motive, a place of death, a time of death, a cause of death, the mechanics of death, the circumstances surrounding the death, a confession and an eyewitness, then unless the words came from the defendant's mouth premeditation would appear not likely be proven to have existed for an instant or otherwise.
Additionally, the words in the legal definition are deliberation and planning. The definition for both of those words indicates that this is not an "instant" process. Although the definition states that it depends on the circumstances and the person and indicates that it could be "instantaneous", those two words indicate that it can not be so.
Still, the key thing is to prove it in court, and that means the prosecutors must prove deliberation and planning beyond a reasonable doubt.
As for the defense trying to exclude Mothers from the jury, I could not agree more. The next best group to exclude would be women, any model will do.