I don't think so...
But the 24 hours are actual uptime, i.e. if you shut your system down, the countdown stops
ok... i shut it down until i pay ...
no, just demo you will do this methode.
if, you are not ready to buy new key for now, you can continue with 'demo key', just login to account server at mikrotik.com and make demo key, that server will send mail you 'demo key', than paste it into routerOS. i think you will access to your router is not 24hours.
keep it your software ID