Why wait?  Use MicroPitch, H910 H949, or maybe HarModulator.  Set up WET1 DRY 2 (or the reverse).  DELAY(s) from 3 to 60 ms.  PITCH(es) to taste.  OUTPUT LEVEL as appropriate.

Yeah, actually Eventide designed the first doubler effect. It was even used in the riff on AC/DC’s “Back In Black”. 

I would recommend you try the factory presets "BACKING VOCAL" and "FAT H910" in the H910/H949 algorithm.