I was able to reserve a Cabana for a 4-hour block for an upcoming flight. Do I have to show up right at the beginning of my reservation time, or will it be given away at some point?

I'm connecting from T3 to T5 (not sure how long that will take), and might want to partake of dining in the main CCR area before catching a nap in the cabana, so wasn't sure if it mattered what time I actually show up to claim the cabana.

Thanks!