It is possible to extend the free trial of 180 days license period. Please open the CMD (Command Prompt) as Administrator from the server and copy paste the below command or write without any mistake and hit enter.
slmgr.vbs -rearm
That is it. Now it will ask for a reboot/restart. Please restart your server and claim 180 more days for free.
Question - How many times can i claim extra days or extend the trial period?
Answer - We are not sure about this. It depends on Microsoft.
Please note:- You agree to use this trial for your testing projects only. Make sure you do not violate Microsoft's terms regarding this product. If you really wish to use Windows OS for your project and not using this OS for a testing purpose, please buy a license key from us or Microsoft.
Enjoy
Source:- Online/Microsoft.