Comment by shiroiushi

Hibernate mode takes a long time to enter and exit, as it involves writing a lot of data to disk and then reading it back upon resuming. The whole point of Sleep mode is that it's fast: you just close the lid and you're in sleep mode, saving power. Then if you want to check something quickly, or resume your work, you just open the lid and in a few seconds or less, your computer is fully operational again.