You may upgrade until the roster is locked. Then it will balanced and updated. I don't have a definite day on locking it but expect the middle of next week.
Only problem with suggesting a 6 or 12 hour war, is that it's usually scheduled on US time. Which is all well and good if you live in the US. At least in a 24hr war all time zones get a chance to make their plunder etc. The Zodiac wars, when postponed were awful for some of us, they started on Mother's Day and finished on Monday for my RS and I and that made it hard to participate properly. Just gotta remember it's a worldwide game and not just the US like it.