I know you're excited, but wait a couple extra days for the dust to settle and then apply. Better to be safe than sorry
You can just ask a CSR how many days it's been. I'd also wait for your 2nd statement, and make sure you don't have a balance.
So this applies only to Amex and no other credit card?
AFAIK, yes. Other lenders (like Chase) allow you to request a CLI the same day your card is approved. Others have you wait 6 months or a year. YMMV.