There is no set time limit, and what counts as reasonable depends on the circumstances
A card with a power level appropriate for Modern might not be fit for Standard
Mickey Mouse, Brave Little Tailor translates as a 5/5 Flying creature in Magic, but with eight converted mana cost, he's far worse than a Shivan Dragon
You'll know these cards by the Planeswalker symbol located in the lower-left corner: As we covered in our first look at the set, The Lord of the Rings: Tales of Middle-earth cards will be legal in Modern, Legacy, Vintage, and Commander
Nameless Race is just that, the total opposite of shapeshifters with changeling and cards like Mistform Ultimus
Make sorting cards part of your routine I usually sort mine on Saturday or Sunday and almost always after 10 PM