SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '571c47608782cdbfef616bdd00695b3dcc472b55054724a88d3624e263f44555' 
  AND token = 'mQvumbjBBtp3FkRXgeoOkDgHezhGtxdzYXsDJ+9G+NE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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