Can anyone tell me what constitutes a "same day standby?"

Specifically, I am booked on CO1094 (LAX-IAH), which departs at 12:30 am, so I'd actually arrive at the airport on 3/29 for a flight on 3/30...

If I would like to take CO1694 (LAX-IAH), which departs at 6:30 pm, would I be able to do so on 3/29 as a same-day standby?

Thanks for everyone's help in advance.