Quick way to max the maturity of your favorite cards.
If you have either multiple devices or multiple accounts, when the daily maturity boost for your leader comes up, accept it, then change your leader to something else, then gift your card to a different account. Switch to that account, accept the gifted card, then set it to your leader. Click the daily maturity bonus. Rinse and repeat. I maxed my Beowulf and Amdukias quickly like this, now I'm working on my Forneus.