What is the minimum time the vegetables must marinate to become pickled? Thanks!

This is a great question! I'll amend the recipe to state the time. I usually make them at least 1 hour before serving, but they get better the longer they pickle. The recipe makes enough for several batches of tacos, or whatever else you want to serve with banh mi flavors. They last for a few weeks in the refrigerator.
Thanks for asking, and for making them!

Thanks so much. I prepared thrm this morning for tonight, snd they are finely cut, so we should be ok :)

Depending on how thick the vegetables are cut. If they are matchsticks, 2-3 hours is is normal. Thicker (think french fry -sized), will need 1/2 day-over night. I would taste one or 2 after a few hours to see if the pickling solution penetrated.

Because the liquid isn't heated, it takes a little time. You could easily make them the day before or morning of, but doing it immediately before will just get you veggies sitting in brine. They are delicious tacos. I make them often.