A month or two is my rough guess, i have had chickens about this size and it took them a while to start laying.
22-28 weeks is a good range of time in which you might expect to see eggs - some will lay sooner, others later - but this is a nice window of "average".
My SS was about 20 weeks when she began laying and once she began, she laid nearly every day. I was sorry to have to re-home her and still miss her - but she terrorized the other hens.
Wow. Thanks for all the input you've put in this thread guys. I'll update here once she laid her first egg