I clocked my layout loading time around 4-5 seconds. My processor is not one of the best. I have 3 panels with lots of buttons, labels, and few other components. I like to keep my project simple and gather all components in 1 form. Is this bad practice. I never expected the delay to be that long.
I can't really tell you what is good or bad practice, except that if it works and achieves what you set out to do, it can't be bad.
I had the same problem with an app when I first started, now what I tend to do is load the layouts for different elements in-line as they are required. You can check most items with isinitialized to see if they are already loaded, and load them if not.
It's not really too cumbersome and saves the long wait when the app first loads.