The clan lb updates at the sometime everyday ( midnight pst ) it just varies on the time it takes to show the update. Usually a few hours. Have your clan members be in your war clan before midnight pst and you should be fine
Definitely support the clan rank update as close to match up time as possible. Also once matched the roster should lock both in and out to maintain the same ranks and Rosters for both clans. Let's keep these wars as free of Roster manipulation as possible