By "no guarantee" I mean I have given you my opinion only. As writers on this forum we only give opinions - most, hopefully, are technically correct but occasionally some are incorrect.
The device operates at zero cross-over point. In any full cycle there are 2 cross-overs, 0 degrees and 180 degrees. Assuming your trigger has just missed a cross-over, the turn-on will not occur until the next one, which will be just under one-half cycle into the future. At 60Hz the period is 1/60seconds = 16.666 mS, so 1/2 cycle period is 8.333 mS. Hence, if you just miss a cross-over point, the next one will be a maximum of 8.333 mS away (ie the delay time)