Things I learned early on while browsing steemit.
- If you upvote before 15 minutes you give 99.94% to the author and get 00.06%
- If you upvote after 15 minutes you give 50% to the author and receive 50%
- If you upvote after 30 minutes you receive 100% curation reward
If you upvote a lot in a 24 hour period each of your upvotes are worth less and rewarded less as well. The recommended amount of upvotes in 24 hours is 20-30.
So in conclusion, its good to vote early, but it's also good to wait a good 30 minutes for maximum profitability.