The message just means if you can not get your EAD approved in 90 days. you can do nothing except waiting.
There mighe be some gap bewtween your current EAD and previous EAD if your EAD renewal can not be done in 90 days. During gap, you might not be allowed to work. In the past, you could go to local office to get a temporary one for the gap period if any. But now this policy is cancelled.