My very last Monarch caterpillar is pupating today, so I think you're in the tail end of the bell curve. If you bring the caterpillar indoors, it will go a bit faster because of the warmer temperatures. From egg to caterpillar is about 4 - 6 days. From caterpillar to
chrysalis is about 15 days. Eclosure follows in about 14 days. If your "cat" is large, it is probably in the last instar...