SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '875f403bcc6f4c26b44f771d4fc575f85771838099d31910bc693582ab295ce4' 
  AND token = '9b6+IXdL+w4pmurohFZDvUFfuh5ZYOm4JuRgZ5TYEdQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00039

JSON explain

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