SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '8a4839dc10d72ef0e1edbad83e011073131803f2d63fdbb885da1394352e24bf' 
  AND token = 'I/nlbudoTlNIkrb9p/fYdtjyxbehoLjPib2Nz69OS0c=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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