As far as I know, the power device in most SSRs is a TRIAC. So, same as a TRIAC, a SSR can be triggered anywhere in the wave, but you have to wait until current reduces to zero in order to achieve turn off.
The main reason for using a SSR instead of a TRIAC (which is cheaper) is when you need to isolate the control circuit from the load. In fact, the SSR has built-in optical isolation. And some of them include added circuitry to delay turn-ON until the next zero voltage crossing (synchronous SSR).
More on this: www.omega.com/temperature/z/pdf/z124-127.pdf
Is this what you needed?.
Yep, that answers that. I was under the impression an ssr did not contain triacs.. that they used two scrs along with some other magic which could cause them to have different properties. Thank you