SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '342a7604766bf3f40c31fb0f37dfdec2b8150632d6a20d6dad6ec8f30488fde4' 
  AND token = '0+BR8h6jLwgV6LjVCFzOgZQEMsn3tkbHyM8gbxeRXqQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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