Type the Alphabet - as fast as you can!
HTML (JavaScript (ES6)), 129 126 117 bytes



&lt;input id=i onfocus=l=0,n=Date.now onkeypress=event.which-97-l?i.outerHTML='Fail':24&lt;l?i.outerHTML=n()-t:t=l++?t:n()&gt;




Click in the input and start typing! Also, my typing sucks; I take about 5 seconds even with practice. Edit: Saved 2 bytes thanks to @HermanLauenstein by switching language. Saved 3 bytes thanks to @qw3n. Saved 9 bytes thanks to @tsh.