Reduce Hero Regenerate Time
Whether you use Heroes or not, they are useful to have in battle and would like to be able to use them more often in battle. Even though the times have been previously reduced, they still need to be reduced more. The stronger your Heroes become, the longer the wait and the times are just ridiculous. My suggestion would be to just have a flat rate, regardless of the level of your Hero. I think 20 minutes would definitely be much better and allow for more usage of these very expensive units.