How long can ISO 400 film run for at f/13 in total darkness before it over-exposes?

Hi. Hope you can help me. I was planning on going out and shooting some star trails on such a lovely clear night. The camera is fixed at f/13 and the film is ISO 400. What is the maximum amount of time I can leave it running for on bulb mode before things start to go wonky? Many thanks in advance.

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia…).