Simple HODLer contract. Written in 10mins. Passed static analysis but is not guaranteed to be safe.

HODLer.sol

pragma solidity ^0.5.0;

contract HODLer {
    
    
    uint releaseDate;
    address owner;
    
    // Contract deployer specifies deposit release date in constructor
    constructor(uint secondsSince1971) public {
        releaseDate = secondsSince1971;
        owner = msg.sender;
    }
    
    // Anyone can deposit simply by sending ether to the contract address
    function () payable external;
    
    // Only owner can withdraw all Ether after releaseDate has passed
    function withdraw() public {
        require(msg.sender == owner);
        require(now > releaseDate);
        msg.sender.transfer(address(this).balance);
    }
    
}