SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6cda351eebede32472a5eecbd462476e24438482871b91bb3a1862970cfb4476' 
  AND token = 'oUV/gXNQBjRGQHXSdoq1xEWfwDESdmzGvoRKRj+PjZs=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00036

JSON explain

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