Can a triac which is driven by another triac be used for switching AC continuously?
This is exactly how it is done.  Your circuit should work fine.  There isn't much worry about the off time, since the parts will be off near the zero crossing, the current involved will be small.  However, the zero-cross circuit may make the turn-on time longer than necessary, I don't know.

Also consider that most loads will have some inductance.  The effect of this is that the voltage the triacs see will not be sinusoidal, but will go from zero to some non-zero value instantly at turn-off.  This works in your favor for a faster turn-on.

Again, all of this switching occurs at zero current, so it won't be noticable to the load.