SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '31d3ce2900396122039a5fca95ceccc0b36324e768296122764bb26e00031cfd' 
  AND token = '0dALDr+lcAkf0v3YZMBfpLdDSv2AswlP9mbxSuvxOf4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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