[gavinflud]

Funnily enough, I recently had to help with an issue where a company's payment screen was not loading correctly and instead displaying "Invalid session". They use a third-party vendor to handle payments and display their payment form in an iFrame on their website.

There is an initial request to create a session that has to pass the desired expiration time of the session. Unfortunately, the vendor requires the time to be in Eastern Time. The poor, naive soul that originally implemented this just got the current date, added 15 minutes, and converted it to "EST". As soon as daylight savings hit a few weeks ago, the expiration time was automatically being set to 45 minutes in the past, the vendor was responding with "Invalid Session" and the company was unable to take payments from customers.