When a freeday is requested, it is IMPLIED to last for the rest of the round, just like when a CT gives a freeday order, it is IMPLIED to last until the end of the round or until a CT revokes the freeday. It's a freeDAY after all. If you guys need an official rule on this, fine, we can throw in another JB rule to patch up stupid loopholes like this.
And that's exactly what this is, a loophole to the rules, because clearly the only reason why this situation exists is for CTs to trick Ts into getting killed, which is not okay. Because why would a prisoner want their LR to be a freeday that lasts for only a few seconds if not specified? Obviously they want a freeday for the rest of the round. Are we going to start killing prisoners for requesting s4s as their LR if they don't specify that they want to do s4s until someone dies? Are we going to start killing prisoners for requesting gun toss as their LR if they don't specify that the winner gets to kill the loser? Of course not, but apparently it's okay to kill prisoners who want a freeday as their LR because they didn't specify that they want it to last for the remainder of the round, which is a total bullshit excuse to justify a freekill.
Yes, we don't have in-depth specifics pertaining to Last Request rules yet, but that will change soon. Until then, it is absolutely not okay to kill a prisoner who is granted a general freeday LR.