90 days.
But it isn't really recommended to reject a card like that, the limit goes up pretty quickly in the case of AmEx.
Sometimes within 2-3 months if your spending are good.
But the good part is the wait time is only for that specific card.
So you can apply for an MRCC card instantly, start spending, and build a good credit profile with AmEx.
And when you're ready for Plat Travel next, your limit should be much better! 🙂