I can see the need for a time limited LiveCD that has propriety software outside of the GNU/GPL. In effect propriety software could piggy back with the GNU/Linux distribution without inhibiting the OS. The maintainer would just time lock or encrypt the software package not the OS.
This is done for a lot of live systems in use today. The devices are allowed to function after the time out but most are crippled in some functionality form or just disabled some way. Encryption and just time locking can be done for any application. But the OP should be aware there are means to defeat these techniques.
If you have to ask a 'LinuxQuestion' forum about how to do this form of protection then your not really able to carry them out anyway.
I for one won't be giving advice other than what I've given on this subject.