I don't see a delay, as soon as I click, it opens the box.
HOWEVER there are 2 things you need to modify for a nice click + unfolding experience:
- in order to avoid any "jump" and glitch in the unfolding animation, the element that will grow from height:0 to height:auto has to have NO margins or padding whatsoever. Prefer using a totally blank div, don't give it any style or border. Add a div inside to which you'll give margin pading border color etc.... but the div that's unfolding, leave it with only the height property.
- in order to have the text/content being masked during animation, give this unfolding div the paramaeter overflow:hidden so the overflowing content will be masked.
Can you tret these 2 points, test again and come bacl if you're still witnessing a delay?