Manage evm_setTimestamp RPC call provided by the modified testrpc from https://github.com/Georgi87/testrpc

setBlockTime.js

function rpc(method, arg) {
  var req = {
    jsonrpc: "2.0",
    method: method,
    id: new Date().getTime()
  };
  if (arg) req.params = arg;

  return new Promise((resolve, reject) => {
    web3.currentProvider.sendAsync(req, (err, result) => {
      if (err) return reject(err)
      if (result && result.error) {
        return reject(new Error("RPC Error: " + (result.error.message || result.error)))
      }
      resolve(result)
    })
  })
}

// Change block time using the rpc call "evm_setTimestamp" available in the testrpc fork https://github.com/Georgi87/testrpc
web3.evm = web3.evm || {}
web3.evm.setTimestamp = function (time) {
  return rpc('evm_setTimestamp', [time])
}