I was always under the assumption that trial softwares write a registry value of the installation date and then the software makes a comparison of the current date of the system with the remaining days + installation date to verify whether the trial period is still valid or not. If this assumption is to be true, winding your system clock further up ahead than the remaining days should end the trial period of the software (or keep winding the clock backwards to use the trial software as long as you wanted to). From experience, This was the case for some softwares, not so for others.
For the latter case, I noticed that the trial period expires only after the days have passed in real time. I confirmed that the software wasn't connecting to the outer network for validation mechanism, so it is definitely something being done locally on the computer. How does the trial period validation work in this case?