I know from my prior Synchrony accounts that they report new accounts quickly, usually within 2-7 days. My new Sam's Club Mastercard is the fastest I've ever seen - showing up 24 HOURS later on both Experian and Equifax. Have not yet checked Trans Union. Wow! They have all the makings of a Barclay's Bank, who is also a fast reporter.
Alternately, Synchrony can be a fickle animal sometimes - when receiving a CLI, they will sometimes do mid-cycle reporting so it shows up quickly (i.e., when they increased my AEO Visa to $15,000, the new limit was showing up on credit reports a week later), but other times for the same card(s), they will not report the CLI until the normal date that credit card reports to the bureaus. Funny.
I try to pay charges as soon as they post to my Synchrony cards, as sometimes the occasional mid-cycle reporting can be a surprise. Surprise - we just reported your $300 balance on a card midcycle and decided to report before the normal reporting date to the bureaus - when you had planned to pay it off before the statement and didn't expect surprise midcycle reporting. This has only happened once, but it's not a fun surprise. 
It seems to be reporting within 24 hours for most of us to EX and EQ only. if someone could please report back re/ how long it take to hit their TU report, that would be great!