Why is it that when I engage an Onslaught, sometimes I have the option to send the attack when we are ready, and other times we have to wait for the timer to expire ? What am I doing wrong/different when I start an Onslaught ?
Upgrade your War Bloc building. You'll need Warriors Drafts and the required resources. It can take awhile so a good supply of boosts would be in your best interests too.