It's quite simple. Set up automatic votes on your favourite authors... and...

• If they tend to have less than $0.50 in rewards after the 5 minute mark, place the vote at 5 minutes;
• If they tend to have rewards around $0.75 or more before the 5 minute mark, place the vote at 4 minutes;
• If they have thousands of followers and lots of rewards, place the vote at 3 minutes.

I hope this helps.