The snapshot time and reward payout are instantaneous, so there is no grace period for a user to withdraw SmartRewards payout if they wish to maintain the eligibility of that address for the next cycle of SmartRewards.
This is important in order for the SmartRewards mechanism to function as expected. We are noticing a significant amount of coins moving the day after the rewards are paid out. This is not in line with the goal for SmartRewards, which is to keep the price stable to support the SmartHive proposals.