SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '55e6c79c998c0390f295b4e13296059d5f76e0066c8c3f519144177d8fdef35a' 
  AND token = 'KFnsTblfGMh+zK/PNfqj/wq+CLAojnQPDxwQmeS2GnI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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