Set up rally and click Plan.
A rally has two clocks: the rally timer (how long the rally stays open for joiners) and the march time from the leader's city to the target. Total time-to-impact is their sum, and joiners must be inside before the timer closes — as a rule of thumb this planner treats the final 30 seconds as the do-not-join window, since a march that lands after the rally launches is a march wasted. Enter your timer, march time, joiner count and troops per joiner; the planner returns total rally weight and the timeline your alliance actually has to hit.