With a decent ECR and some luck, you might be able to get 8-10 chests with around 1-2 hours of play. So for yourself, if you are not pushing to Silver 1, I would recommend staying in Bronze league and farming the chests there.

Currently (without renting cards) my max tier is Silver III. Nowadays I very rarely reach it. Today I played Splinterlands for a little bit more than 30 minutes, and I earned four focus chests so far.

Good luck and have fun.