How long does the Jelly like substance stay in a kangaroo's pouch?

There is no jelly-like substance in a kangaroo's pouch.

Inside the pouch is dry and warm, and secure for the tiny embryo, which initially resembles a blob of jelly. It stays attached to the mother's teat for several months, until it grows into a joey large enough to begin leaving the pouch for short periods of time. In all, the joey stays in the pouch for about eight months (235 days), depending on the species.