SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '8c6af6ae29f6f6475e15114bbeb55bdc95442a2cef7c29a10f8a350e1f503b15' 
  AND token = '6BkLZr344lmQzem+m6jnusr0rEM40KyteSUrtdyAJTw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00033

JSON explain

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