When you do it actually doesn’t really matter, just do it when you know you have the time to actually finish it and keep downtime as low as possible. There is no grace period for down time after an update, so there is also no reason to wait for that.
Keep in mind that after a bit of downtime your node may take a while to get traffic again. Up to 2 hours. This is because when the satellites notice your node is down during an uptime check, they don’t suggest your node for transfers to uplinks until it’s online again during another uptime check. Just make sure the dashboard shows online and then keep it online and traffic will return in a bit.