Yes, please check the megamenu.css file lines 139 and 151, just change values of Transitions ease.
-webkit-transition: opacity 250ms ease 250ms, max-height 500ms ease, visibility 0s linear 500ms, top 0s linear 500ms;
-moz-transition: opacity 250ms ease 250ms, max-height 500ms ease, visibility 0s linear 500ms, top 0s linear 500ms;
-ms-transition: opacity 250ms ease 250ms, max-height 500ms ease, visibility 0s linear 500ms, top 0s linear 500ms;
-o-transition: opacity 250ms ease 250ms, max-height 500ms ease, visibility 0s linear 500ms, top 0s linear 500ms;
transition: opacity 250ms ease 250ms, max-height 500ms ease, visibility 0s linear 500ms, top 0s linear 500ms;
border: 1px solid rgba(0,0,0,0.3);
border-top-right-radius: 3px;
border-bottom-right-radius: 3px;
border-bottom-left-radius: 3px;
}
.accessible-megamenu .accessible-megamenu-panel.open {
visibility: visible;
top: 3em;
max-height: 1200px;
opacity: 1;
z-index: 1001;
-webkit-transition: opacity 250ms ease, max-height 500ms ease, visibility 0s linear 0s, top 0s linear 0s;
-moz-transition: opacity 250ms ease, max-height 500ms ease, visibility 0s linear 0s, top 0s linear 0s;
-ms-transition: opacity 250ms ease, max-height 500ms ease, visibility 0s linear 0s, top 0s linear 0s;
-o-transition: opacity 250ms ease, max-height 500ms ease, visibility 0s linear 0s, top 0s linear 0s;
transition: opacity 250ms ease, max-height 500ms ease, visibility 0s linear 0s, top 0s linear 0s;
}
I hope this help you.
Regards.