Magento 2 convert date to timestamp using best practice.

Magento 2 You can Converts input date into GMT timestamp using Magento\Framework\Stdlib\DateTime\DateTime Class.

You can set easily convert timestamp using core PHP by function strtotime().
like, strtotime(‘+1 years’);

Using Magento You can Converts input date into GMT timestamp by using Magento best practice way by injecting class dependency in the construct method.

call from template or any other function,
echo $this->convertGmtTimeStamp();

Output in timestamp:
1558310400