SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6b0a9b82f517cd9339e55c05cfc768d9bf278c7af200a4d7bcc1440139052980' 
  AND token = 'mkKEwpM637qPDDtmqPdHU6gLXMEd+gjiMvmvfJ7NMyg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}