Before I begin to explain the premise, I have already considered doing it in small chunks in intervals or in real-time, but both of those methods will require a lot of code re-writing.
Currently, the credits screen for my project is about 7,000 characters, and I want each spritefont character to be a separate object, rather than a single block of even a line at a time. Of course, at the start of the layout, the loop that requests "credits.txt" runs 7,000 times, and the game hangs for about two seconds while it's loading. The benefit to this text file is that I can edit the credits any time in a very intuitive way inside the text file, rather than doing it line by line in the events editor. I do have a copy of the spritefont outside the layout as is normally recommended with sprites (to prevent short stutters when a sprite is created for the first time), but I don't expect it's doing much to help.
There is an excellent tutorial about creating a new "loading" layer on top of layouts so that the player doesn't see the ugliness of a game chugging along while sprites load. While that will require some tinkering to get working, I'm happy to do it. But I would love to know about any other potential options I have in forcing a layout to wait until all objects are loaded before it beings "playing."