Slings harden up pretty quickly, I've seen a 1 inch E. cyanognathus eat within 24 hours of completing a surprise moult (left a pre-killed mealworm outside the burrow, checked back 24 hours later to find it sat next to its exuvia munching away on the mealworm).
4-5 days should be long enough, I usually dig out a freshly moulted prey item for the first post moult feeding, it won't even attack the cricket it if it isn't ready, just pull the cricket if the sling doesn't eat.
What size? I'd give it a cricket after four days but you could always wait a 2-3 more to be on the safe side as it is a more expensive T plus a ravenous T will make a pretty cool attack. I've heard of folks feeding slings a day after, I wait at least three.
I usually offer slings food about 5 days after a moult - a week sounds fine. There are always gonna be a few anomalies, but 7 days seems on safe side to me.
Since my slings always tended to burrow, getting a good look to see if their fangs had blackened just wasn't always possible.
If you're really in doubt, offer something soft -- like a newly moulted white feeder, or my old standby: waxies.