SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '521fa40d2b41d3d4f1c676251e0a1c9670505dc14ef892e99a3eb526bf889735' 
  AND token = '5lwf9BFfuDNNDIGvcGbSkFgxDLERgieAVp6zykTW+FY=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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