Say I am writing an extensive novel about Creepers in a book in Survival. Should I worry about crops growing, furnaces baking, the sun setting, etc.?
No, time doesn't pass while writing a book (in singleplayer). Most interfaces won't pause time, such as looking inside a chest or using a crafting table, but a Book & Quill is an exception to that rule.
You can test this by making a new Creative world, using a spawn egg to spawn in some mobs, and then opening a Book & Quill. All the monsters you can see around the edges of the book-writing interface will be frozen.
(In multiplayer, of course, no interface pauses time.)