Last I checked SportsBook was still a Merge skin. Poker cashier withdrawals are processed by the Merge network, no matter whether from Carbon, BlackChip, SportsBook, or any other Merge skin. Only those skins with a casino or sportsbook cashier that let you transfer poker funds over and withdraw there do not go through Merge.
So if you're using the poker cashier then you're going through the same queue as Carbon and the rest -- SportsBook isn't doing it any faster. Sometimes it takes 2 weeks, sometimes it takes 8 weeks. Sometimes the checks bounce and have to be resubmitted (which by the way happened with Stars and FT too, they were just quicker about it). The norm is currently 3-4 weeks I'd say, but there are still folks who requested withdrawal in April who still haven't received theirs, while others sometimes take only 2 weeks total.
It's frustrating yes, but such is the state of poker withdrawals in the US. Your best bet is to use a skin that supports WU withdrawals if you really need it fast, but those aren't without the occasional glitch and long wait too.