The key conditions that permit based on the current time (i.e. "Permit if the customer is visiting before [or after] a certain date and time") are now much more operationally accurate.
Previously, the time logic was based purely on theme Liquid code – and, as such, Shopify's storefront caching would get in the way. For example, if a key permitted access starting at 3pm, a visitor arriving at 2:59pm would be denied access – and then would likely be again denied access at 3:01pm, because Shopify would serve them the cached copy of the storefront that was generated at 2:59pm.
To get around this, Locksmith now automatically runs an install 30 seconds before the configured date and time. This way, the cache is forced to reset, resulting in a fresh rendering of the page, which in turn results in the visitor being correctly granted or denied access.