I understand now, thank you.
Right now the capability of the Triggers engine is fairly limited when it comes to executing a trigger with multiple conditions. We're going to me making improvements to this in the future so it can handle things like multiple conditions, more complex Boolean logic, etc.
In the meantime you could hack it if you offloaded one of the conditions to your Arduino sketch file where you have the fully ability to run custom code.
I'm thinking something like using Cayenne's trigger engine to set a Virtual Pin value when the temp is lower than 25C. Then your sketch code could monitor the value of the Virtual Pin, and when it is a certain value, it could also check the time and only change the state of the actuator from the sketch code when both conditions are met.
There may be a more clever way to do this, so I'm open to other suggestions from the community!