You should try calling them - I find that with any website they are insufferably slow to respond to emails, so I try to call. I do know that the last time something was returned to JAX (the store erroneously sent an item to JAX when they should have refunded me immediately in-store), it took over two weeks from the date of arrival for "processing." Like from the time it was shipped (9/14) to the time I saw my credit come through to my cc (10/11) it was almost a month.
Soooo, I wouldn't count on getting your GC credited by this Thursday, but you could call and find out either way!