The Pattern is already straining to contain the chaos unleashed by The Dark One. I think her fear is based out of the very real horror that if we're only seeing the tip of the iceberg, with mass starvation, warfare brewing with the Seanchan, Shadowspawn and the Forsaken, and the instability of reality, they may not be able to survive long in a world with the Dark One fully unleashed. They may truly need as much time as possible to prepare.

Personally, I think Rand just wanted to give Egwene a reason to coordinate all of the allied nations, and I don't think he means to confront her about it. The last Seal may very well be destined to fail at precisely that time without Rand doing anything, making consternation over Egwene's thought that this is a very bad idea (this also includes Perrin, Mat, Elayne, the Wise Ones and pretty much every leader we're in close contact with - well maybe not Perrin, but we won't know how this pans out until the actual scene).