Hell, I'm in a giving mood.
Here's what I do:
When my season ends at a specific level, I look to see who would start the next season at a higher level. They get promoted right then.
Season rolls, I resign my minor league FA and place them appropriately. My real prospects are already where they need to be.
Spring training plays out.
IF I need players at a certain level to meet minimum requirements, I promote the most "seasoned" minor leaguers to the next level. The system politely, and quietly, keeps count of how many active and inactive players I have at each level. I make note of that and adjust accordingly. Takes me somewhere between 4 and 7 minutes to get everyone where I need them.
I'M A GODDAM ROCKET SCIENTIST BECAUSE I WAS ABLE TO FIGURE OUT HOW TO DO THIS WITH STRESS!!!!