One thing homeassistant is really missing is a simple UNIX time sensor. What drives me to open this feature request is an issue with an automation for SpaceX rocket launches. People are trying to get an automation to work and there is way too much fiddling goin on:
SpaceX has a REST Api that provides launch times but it is in UNIX time. When it comes to templating a time based sensor without entities theres always a struggle if no entities are involved in the sensor that updates the state of the template sensor. See Template - Home Assistant
So basically if you want to match a UNIX timestamp you need another sensor that triggers it every secons so that the template sensor updates its state to functions properly as a trigger.
Also I think that UNIX time is a common format for dealing with timestamps and currently there is no method to use these timestamps as triggers (at least I am not aware of one)