Generally in their second or third year. It depends on the variety.
Some pump out offsets like crazy, others will put out maybe one or two a year after a couple of years. I have one species semp whose name is escaping me at the moment since 2009 and have only received maybe two offsets total among 4 or 5 rosettes. I took other steps to increase them last year because I was worried about flowering. I think it is S. degenianum, a very nice looking species.
Be patient. Soon you will be overrun with the cackling and need earplugs.
