SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '312410f38902afa974354122108e75c40293faa5eb367bc175e7c9a6fc85978f' 
  AND token = '96YI1qgmCb56PF8BRT4xjNYDAGgMNBUCKT/SaanfAjs=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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