When should ginger beer's second fermentation start producing pressure?

I am trying my first batch of ginger beer, using what seems to be a pretty standard fool proof recipe.

For the bug:

2 cups filtered water; 2 tbsp chopped ginger; 2 tbs refined sugar

The ginger wasn't labeled organic, so I peeled it. The fermentation started slowly, but by day 4, it looked fizzy enough to use. The first day had a cheesecloth cover, but then my airlock top arrived, and I switched to that. I bottled on day 4, but now on day 5, the bug is really active, and I wish I would've waited.

For the brew:

2 quarts water; 273 grams sugar; 54 grams ginger

Brought this to a boil, simmered 7 minutes, let fully cool to room temperature (paying attention to all of the warnings about the heat killing the yeast), strained, and added:

1/2 cup of the bug (strained); 150 ml lemon juice

bottled it up into sterilized swing-tops, only filling to the shoulders of the bottles, for headroom. Set them into the handily divided, cardboard shipping boxes from the swing-tops.

This morning, I went to burp the swing-tops, and the bottles seemed FLAT. I didn't hear any pressure, and didn't see any bubbles. When should second fermentation start producing some bubbles and pressure? Should I just be patient? Would it help to add a splash of the now more active bug to the bottles?