You can use a demo license to install Platform LSF and get it running temporarily, then switch to the permanent license before the evaluation period expires with no interruption in service.
Although there may be exceptions, a typical demo license:
Is used during your free evaluation of LSF
Expires on a preset calendar date (30 days after the license was generated)
Is file-based (does not require Flexera® FlexNet™ software)
Licenses all LSF products
Allows an unlimited number of hosts to be LSF servers