Infinite Tapestry says Time & Matter Effects are +1 difficulty in the Umbra.
High Umbra - Infinite Tapestry pg. 24 says navigating most of the High Umbra is Perception + Cosmology. Navigating higher realms is Intelligence + Enigmas.
Middle Umbra - Infinite Tapestry says Middle Umbra navigating is Intelligence + Cosmology between realms, Wits + Enigmas within a Realm.
Infinite Tapestry pg. 118 states single Sphere Effects in a Shade or Shard Realm are -2 difficulty for the realm’s Sphere. -1 for conjunctional Effects using that Sphere.
Etherspace - Infinite Tapestry: magic is difficulty Arete + 3. No Paradox. Botched effects backfire but don’t create Paradox. Pre-existing Paradox Flaws disappear but reappear when you re-enter Earth. Rather than gain a flaw for Paradox, gain Quiet that disappears when leaving that area/realm.