Now

You can obtain the starting time of the current block using the function Tezos.get_now from the standard library. This timestamp does not change during the execution of the contract. Please be aware that it is up to the baker to set the current timestamp value.

const today: timestamp = Tezos.get_now();

When testing your code, the LIGO CLI option --now allows you to control what Tezos.get_now returns.