I've only had same day weigh ins, and have had to cut for them...often leaving a hydrating and food fueling window of no more then 3-4 hrs. It sux as it leaves you in a weakened state and at more risk of harm, for reasons previously stated. In ams though, this is the window you get as time is a luxury not afforded us. In the pros it's a different deal..it's your job and livelihood. As well you are more susceptable to harder shots and longer rounds. So IMO...the longer, the better, the safer.