first, determine your smallest quantization time (sixteenth, eighth, etc.)--how exact do you want "in time" to be. use a metro that continually bangs at that rate, which might be very fast. You can also use [counter] --> [%4] --> [sel 0] to use every 4th pulse instead of every one, etc. If you change the [metro] rate you'll need to be sure it starts its new rate at the right time, so probably a [trigger 1 i 0] where 0 stops it, i sets the new msec rate, then 1 starts it again, or tie it somehow to the [matrixctrl] counter. (that could be used for the quantization too, actually.)

then, instead of your input (keyboard) notes actually sounding right away, store the note(s) in [i] or a message box, and they only get played when you get your overall "timing" bang from the main metro. Of course, this only helps with early notes.