A delay is definitely not going to happen, that sounds infuriating for anyone who actually wants the emoji to show up.
My solution will be to make it so the emoji completion will not show up until a letter is typed. For instance, : won't trigger it, but :a will. That will make spaces not trigger it either. That'll also help prevent it from showing up while writing code.
I've create an issue: https://github.com/NodeBB/nodebb-plugin-emoji/issues/12pitaj created this issue in NodeBB/nodebb-plugin-emoji closed Don't trigger completion on just a colon #12