It means that you have a limited opportunity to get him NOW. They'll do the event two or three more times in the future and then add him to the Gate like everyone else.
SO.. event could be come again (max 1 more time id say, 2 would be very unlikely). you can get him pretty easy now, since u only have to duel assist to get points. when the event has happened the last time there will be something between 1-4 months and he will be added to the gate after this time. so u can farm his cards at the gate & will be able to unlock him through missions - they wont expire!
You can only unlock him now and then the event will come back in 3 months and you will get a second chance. Then maybe 9 months later they will put his unlock mission at the gate. Unlock him now though because sometimes character-specific skills can be super powerful and you won't want to wait 3 months
Anonymous
WolfgangDS
