There are a few libraries that provide the functionality to perform the conversions between the timestamp and year/month/day hour:minute:second including:

• @piper-merriam 's Ethereum Date and Time tools
• SkeletonCodeworks's Date utilities for Solidity contracts

And now there is @bokkypoobah's Gas-Efficient Solidity DateTime Library. More information about it in this medium post.

Warning - Self Promotion

There are a few libraries that provide the functionality to perform the conversions between the timestamp and year/month/day hour:minute:second including:

• @piper-merriam 's Ethereum Date and Time tools
• SkeletonCodeworks's Date utilities for Solidity contracts

And now there is @bokkypoobah's Gas-Efficient Solidity DateTime Library. More information about it in this medium post.