You can say that something is premature when it happens too early and is therefore inappropriate. It now seems their optimism was premature + prematurely prema·ture·ly Holmgren is careful not to celebrate prematurely
Something that is premature happens earlier than usual or earlier than people expect. Accidents are still the number one cause of premature death for Americans a twenty-four-year-old man who suffered from premature baldness. + prematurely prema·ture·ly The war and the years in the harsh mountains had prematurely aged him
uncommonly early or before the expected time; "illness led to his premature death"; "alcohol brought him to an untimely end"
{s} mature before the proper time; untimely, before the proper time; too early; hasty, hurried
A premature baby is one that was born before the date when it was expected to be born. When my daughter Emma was born she was two and a half months premature. + prematurely prema·ture·ly Danny was born prematurely, weighing only 3lb 3oz
Happening, arriving, existing, or performed before the proper or usual time; adopted too soon; too early; untimely; as, a premature fall of snow; a premature birth; a premature opinion; premature decay