Hi KENYONB good to see that it's all working, your game's a good laugh too!
The loading times seemed kinda variable, sometimes it wasn't too bad, other times it took about 15 seconds or something to load the achievements list. Leaderboards seemed to be faster, not really sure why. We're not doing anything complicated in the plugin, it just calls through to the native API that Google provide. So any areas which are could be slow are in Google's hands, so I can't do much about it.
I vaguely recall reading a post online from a developer that said after they had reached a certain number of users it began to work a lot faster. Given the amount of content I had to read online while working out how the API works I could have imagined it, and it's only hearsay at best. But it wouldn't surprise me if apps that are still in testing, have only recently been released or have low user numbers might use a slow path on the Google servers. Although saying that, I just tried to open the Google Play Games App on my phone and it must have taken nearly 2 minutes... This is on a Pixel 2 XL, which is supposed to be the flagship for Android software.
My best advice is to give it a couple of weeks and see if the speed improves. In the mean time I was thinking if you made the buttons react to being pressed it might imply better that it's Google Play being slow, not the game.
The google standard animation for this sort of thing are changing the size ( and shadow if you have one ) of a button to make it look like it's rising from the screen. Another is ripples coming away from the button, but I'm not sure how easy they would be to do in construct.
One more thing that might interest you, not sure if you know yet or not. About a week ago I fixed a bug that was preventing the Google Play popups from appearing over your game. The ones that show you "Achievement unlocked" or "Welcome back". The latest version of the plugin should include that fix.