vmware provides 60 days limits on its freewares(normaly). after 60 days you would not be able to use the product.
That's not exactly how it works. Enterprise products (ESXi, vCenter, ...) will run in evaluation mode for 60 days. Unless you enter a license key, the product won't work after this period of time. However, with registering for the free Hypervisor, you'll get a license key which enables the product for unlimited use with the features included in the free license.
For desktop products (e.g. VMware Workstation), you have to enter the evaluation key which comes with the registration for usually a 30-day evaluation period.
André